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Conductivity and impedance measurements

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These articles refer to ProboStat or other NorECs products, filtered with keywords: 'Conductivity, Impedance'  
ID=400

Electrochemical performance of Co3O4/CeO2 electrodes in H2S/H2O atmospheres in a proton-conducting ceramic symmetrical cell with BaZr0.7Ce0.2Y0.1O3 solid electrolyte

Authors Tz. Kraia, S. Wachowski, E. Vllestad, R. Strandbakke, M. Konsolakis, T. Norby, G.E. Marnellos
Source
Solid State Ionics
Time of Publication: 2017
Abstract The electrochemical performance of Co3O4/CeO2 mixed oxide materials as electrodes, when exposed to H2S/H2O atmospheres, was examined employing a proton conducting symmetrical cell, with BaZr0.7Ce0.2Y0.1O3 (BZCY72) as the solid electrolyte. The impact of temperature (700–850 C) and H2S concentration (0–1 v/v%) in steam-rich atmospheres (90 v/v% H2O) on the overall cell performance was thoroughly assessed by means of electrochemical impedance spectroscopy (EIS) studies. The performance of the Co3O4/CeO2 electrode was significantly enhanced by increasing the H2S concentration and temperature. The obtained results were interpreted on the basis of EIS results and physicochemical characterization (XRD, SEM) studies of fresh and used electrodes. Notably, it was found that the mass transport processes, mainly associated with the adsorption and diffusion of the intermediate species resulting by the chemical and half-cell reactions taking place during cell operation, dominate the electrode polarization resistance compared with the charge transfer processes. Upon increasing temperature and H2S concentration, the electrode resistance is substantially lowered, due to the in situ activation and morphological modifications of the electrode, induced by its interaction with the reactants (H2S/H2O) and products (H2/SO2) mixtures.
Keywords H2S-tolerant electrodes; Cobalt-ceria oxides; BZCY72
Remark https://doi.org/10.1016/j.ssi.2017.04.010
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ID=390

Sm6-xMoO12-δ (x = 0, 0.5) and Sm6WO12 – Mixed electron-proton conducting materials

Authors A.V. Shlyakhtina, S.N. Savvin, N.V. Lyskov, D.A. Belov, A.N. Shchegolikhin, I.V. Kolbanev, O.K. Karyagina, S.A. Chernyak, L.G. Shcherbakova, P. Nez
Source
Solid State Ionics
Time of Publication: 2017
Abstract Samarium molybdates Sm6-xMoO12-δ (x = 0, 0.5) and samarium tungstate Sm6WO12 – potential mixed electron-proton conductors have been studied by X-ray diffraction, Raman spectroscopy, SEM and impedance spectroscopy (in ambient air and in dry and wet air). Solid solutions differing in structure have been obtained in the Sm2O3-MoO3 system at 1600 C. The samarium molybdate Sm6MoO12 has the fluorite structure (Fm3m). The less samarium rich solid solution Sm5.5MoO11.25 crystallizes in a rhombohedral (View the MathML sourceR3) structure. The morphotropic transformation is due to the change in the chemical composition of the solid solution with decreasing Sm3 + concentration. The total conductivity of the cubic fluorite phase Sm6MoO12 at 750 C in air (1.48 10− 3 S/cm, Ea = 1.22 eV) is an order of magnitude higher than that of rhombohedral Sm5.5MoO11.25 (2.34 10− 4 S/cm, Ea = 1.11 eV). At low temperatures (T < 500 C), the Arrhenius plot of total conductivity for Sm6MoO12 and Sm5.5MoO11.25 in air deviates from linearity, suggesting that there is a proton contribution to its conductivity at these temperatures, like in the case of the Sm5.4Zr0.6MoO12.3 zirconium-doped molybdate. Below ~ 500 C, Sm6MoO12 fluorite and fluorite-like Sm6WO12 have identical Arrhenius plots of conductivity in ambient air. The region of dominant proton conductivity is wider for Sm6WO12 than Sm6MoO12, reaching temperatures as high as 750 С for the former. The absolute values of total conductivity obtained for samarium tungstate and molybdate at 400 С in wet air are virtually identical and close to 3 10− 6 S/cm, which suggests the conductivity of both compounds is dominated by protons at low temperatures and the proton transport numbers are similar.
Keywords Phase transition; Fluorite; Fluorite-like phase; Proton-conducting membranes; Proton conductivity; Electron conductivity
Remark http://dx.doi.org/10.1016/j.ssi.2017.01.020
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ID=385

The structural and electrical properties of samarium doped ceria films formed by e-beam deposition technique

Authors Darius Virbukas, Giedrius Laukaitis
Source
Solid State Ionics
Time of Publication: 2016
Abstract Sm2O3-doped CeO2 (Sm0.15Ce0.85O1.925, SDC) thin films were formed by e-beam evaporation method. Thin films were formed evaporating micro powders (particle size varied from 0.3 to 0.5 μm). The influence of deposition rate on formed thin film structures and surface morphology were characterized by X-ray diffraction (XRD), scanning electron microscope (SEM), energy dispersion spectrometry (EDS), and atomic force microscopy (AFM). The deposition rate of formed SDC thin films was changed from 2 to 16 /s. The electrical properties were investigated as a function of frequency (0.1–106 Hz) at different temperatures (473–873 K). The formed SDC thin ceramic films repeat the crystallographic orientation of the initial powders using different substrates and different deposition rate. It was determined that crystallites size and samarium concentration are decreasing by increasing the deposition rate. The crystallites size decreased from 17.0 nm to 10.4 nm when SDC thin films were deposited on Alloy 600 (Fe-Ni-Cr), and decreased from 13.7 nm to 8.9 nm when were used optical quartz substrate. The best ionic conductivity σtot = 1.66 Sm− 1 at 873 K temperature, activation energy ΔEa = 0.87 eV (σg = 1.66 Sm− 1, σgb = 1.66 Sm− 1) was achieved when 2 /s deposition rate was used. The grain size (in the formed SDC thin films) was ~ 83 nm in this case.
Keywords Electron beam deposition; Samarium doped ceria oxide (SDC); Solid oxide fuel cells (SOFC); Ionic conductivity
Remark http://dx.doi.org/10.1016/j.ssi.2016.12.003
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ID=383

Oxygen ion conductivity in samarium and gadolinium stabilized cerium oxide heterostructures

Authors Marius Zienius, Kristina Bockute, Darius Virbukas, Giedrius Laukaitis
Source
Solid State Ionics
Time of Publication: 2016
Abstract Gadolinium (GDC) and samarium (SDC) doped ceria were investigated in terms of multilayer systems, evaporated by e-beam technique on optical quartz, Alloy600 and sapphire substrate. GDC-SDC heterostructures of 1.3 μm thicknesses, composed of 1, 2, 3, 5 and 7 layers and they were investigated by structural and ionic conductivity techniques. Bragg peaks show nanocrystalline state of Gd and Sm doped ceria thin films. XRD patterns show fluorite type structure with space group Fm3m. The XRD analysis of thin films, deposited on quartz substrate, reveals the increase of (220) peak with increasing number of layers. The decrease of (111) peak is slightly notable, also. Thin film heterostructures have a face-centered cubic cell with the following lattice parameters, such as 5.4180 nm for GDC of and of 5.4245 nm for SDC. The scanning electron microscopy cross sectional analysis of three-layered structure clearly indicates the interfaces of different material. There are no visually distinct discontinuities in higher layer structures (5–7 layers). Total conductivity increases linearly with increasing of temperature, but decreases with the increase of number of layers. The highest total ionic conductivity at 1214 K temperature for SDC and GDC thin monolayers was 1.62 S/m and 1.02 S/m, respectively. The activation energy increases with the increase of number of layer as well.
Keywords Multilayer electrolyte; SDC; GDC; e-Beam deposition
Remark http://dx.doi.org/10.1016/j.ssi.2016.11.025
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ID=382

A multistep model for the kinetic analysis of the impedance spectra of a novel mixed ionic and electronic conducting cathode

Authors A. Donazzi, M. Maestri, G. Groppi
Source
Electrochimica Acta
Time of Publication: 2016
Abstract A one-dimensional, heterogeneous and dynamic model is applied to kinetically analyze impedance experiments performed on a novel NdBa0.9Co2O5.6 (NBC) MIEC cathode. The model simulates the spectra in the time domain by accounting for the gas diffusion inside the electrode pores, and for the solid state diffusion of oxygen vacancies inside the bulk of the cathodic material. A detailed kinetic scheme is applied to describe the oxygen reduction mechanism, which includes steps for adsorption and desorption, first and second electronation at the gas/electrode interface, and ion transfer at the electrode/electrolyte interface. The kinetic investigation is based on impedance spectra collected on symmetric NBC/GDC/NBC cells, at open circuit voltage, between 550 and 700C, and 5–100% O2 molar fraction. The vacancies diffusion coefficient and the kinetic parameters of the reaction steps are fitted to describe the data. At the highest temperatures, a sensitivity analysis reveals that the rate determining step is the first electronation of the oxygen adatom, while the second electronation and the interfacial ion transport are kinetically irrelevant. Overall, the model allows to individuate the key parameters for capturing the kinetics of a MIEC cathode.
Keywords EIS; perovskites; kinetics; modeling
Remark http://dx.doi.org/10.1016/j.electacta.2016.11.072
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ID=377

Thermodynamic properties of the Ba0.75Sr0.25TiO3 nanopowders obtained by hydrothermal synthesis

Authors C.F. Rusti, V. Badilita, A.M. Sofronia, D. Taloi, E.M. Anghel, F. Maxim, C. Hornoiu, C. Munteanu, R.M. Piticescu, S. Tanasescu
Source
Journal of Alloys and Compounds
Volume: 693, Pages: 1000–1010
Time of Publication: 2017
Abstract The paper is devoted to the investigation of the thermodynamic properties of nanostructured Ba0.75Sr0.25TiO3 perovskite material synthesized by hydrothermal method. The thermodynamic parameters obtained by a couple of measurements in both isothermal and dynamic regimes (drop calorimetry, solid-oxide electromotive force measurements, differential scanning calorimetry and thermogravimetry), allow for the investigations of the thermodynamic stability in a large temperature range from room temperature to 1273 K. The influence of the oxygen stoichiometry on the thermodynamic properties was examined using a coulometric titration technique coupled with electromotive force measurements. The results are discussed based on the strong correlation between the thermodynamic parameters and the charge compensation of the material system. X-ray powder diffraction (XRD), Raman spectroscopy and scanning electron microscopy (SEM) were used for the microstructure and morphology analyses. The variation of the thermal expansion and electrical conductivity associated with the structural changes has been evidenced by thermomechanical measurements and impedance spectroscopy, respectively. Through a combined analysis of all the results, new features related to the understanding of the strong interplay between the thermodynamic properties, microstructure, thermal expansion and electrical conductivity in the hydrothermally prepared Ba0.75Sr0.25TiO3 perovskite material have been revealed.
Keywords Nanostructured materials; Chemical synthesis; Thermodynamic properties; Electromotive force, EMF; Calorimetry; X-ray diffraction
Remark http://dx.doi.org/10.1016/j.jallcom.2016.09.215
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ID=373

Solid oxide carbonate composite fuel cells: Size effect on percolation

Authors Shalima Shawuti, , Mehmet Ali Glgn
Source
International Journal of Hydrogen Energy
Time of Publication: 2016
Abstract In the studies of solid oxide carbonate composite fuel cell, percolation behaviour of the two phases was investigated as a function of particle size of the oxide phase. The ratio of amount of samarium doped ceria (SDC; Sm0.2Ce0.8O) to Na2CO3 was varied to determine an optimum ionic conductivity as function of oxide particle size. The roles of both phases in the composite electrolyte were investigated. SDC particles were mixed in different amounts of Na2CO3 to obtain composites with carbonate ratios from 1 wt% to 50 wt%. Micro-structural investigations showed that Na2CO3 phase served as the matrix in the micro-structure gluing the oxide particles together. The lowest and the highest carbonate ratios caused low conductivities in the composite as in these samples the 3D connectivity of both phases were disrupted. Low conductivity at both ends of the mixture composition could be interpreted as none of the components of the composite dominated the ionic conductivity. The highest conductivity was obtained at 10 wt% Na2CO3 amount in the composite electrolyte when nano-sized SDC (5–10 nm) oxide powders were used. Two different particle sizes of SDC powders were used to show that the optimum phase ratio, i.e. percolation of both phases, is function of particle size as well. The conductivity in the composite showed percolation behaviour with respect to the two constituent phases.
Keywords Composite electrolyte; SOFC; Interface; Percolation; Carbonate; Impedance
Remark http://dx.doi.org/10.1016/j.ijhydene.2016.07.208, in press
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ID=369

Nanolayered solid electrolyte (GeSe2)30(Sb2Se3)30(AgI)40/AgI: A new hypothesis for the conductivity mechanism in layered AgI

Authors Yury S. Tveryanovich, Andrei V. Bandura, Svetlana V. Fokina, Evgeny N. Borisov, Robert A. Evarestov
Source
Solid State Ionics
Volume: 294, Pages: 82–89
Time of Publication: 2016
Abstract Using the laser ablation method, films comprised of alternating layers of AgI and (GeSe2)30(Sb2Se3)30(AgI)40 glass were obtained. Individual layer thickness amounts to 10 15 nm, and the total number of layers is about 100. X-ray diffraction (XRD) and film conductivity measurements were carried out during several cycles of heating up to 200 C and cooling to room temperature. It was established that after three cycles of thermal processing specific lateral conductivity of the film is equal to 0.3 S cm− 1 and conductivity activation energy is equal to 0.07 eV at room temperature. Attempts to explain such a high conductivity value based on XRD results did not yield satisfactory results. However, our first-principle calculations within the density functional theory (DFT) showed that in the free layer composed of four AgI planes a rearrangement occurs, resulting in formation of the stable structure of two silver planes on the inside and two iodine planes on the outside (I–Ag–Ag–I). Rearrangement of similar stack of eight or twelve atomic planes results in formation of two or three I–Ag–Ag–I layers loosely bound to each other, accordingly. This suggests that increase in specific conductivity growth of multilayer film as a consequence of cyclic heating and cooling may be connected with AgI stratification on its boundary with chalcogenide glass and following stabilization of layered phases mentioned above. The existence of an empty space between the layers that is constrained by iodine ion planes should facilitate silver ion diffusion along the layers.
Keywords Glass-composite; Laser-ablation method; Ionic conductivity; AgI polymorphs; DFT calculations
Remark doi:10.1016/j.ssi.2016.07.004
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ID=366

Tailoring transport properties through nonstoichiometry in BaTiO3–BiScO3 and SrTiO3–Bi(Zn1/2Ti1/2)O3 for capacitor applications

Authors Nitish Kumar, David P. Cann
Source
Journal of Materials Science
Volume: 51, Issue: 20, Pages: 9404–9414
Time of Publication: 2016
Abstract The ceramic perovskite solid solutions BaTiO3–BiScO3 (BT–BS) and SrTiO3–Bi(Zn1/2Ti1/2)O3 (ST–BZT) are promising candidates for high-temperature and high-energy density dielectric applications. A-site cation nonstoichiometry was introduced in these two ceramic systems to investigate their effects on the dielectric and transport properties using temperature- and oxygen partial pressure-dependent AC impedance spectroscopy. For p-type BT–BS ceramics, the addition of excess Bi led to effective donor doping along with a significant improvement in insulation properties. A similar effect was observed on introducing Ba vacancies onto the A-sublattice. However, Bi deficiency registered an opposite effect with effective acceptor doping and a deterioration in the bulk resistivity values. For n-type intrinsic ST–BZT ceramics, the addition of excess Sr onto the A-sublattice resulted in a decrease in resistivity values, as expected. Introduction of Sr vacancies or addition of excess Bi on A-site did not appear to affect the insulation properties in air. These results indicate that minor levels of nonstoichiometry can have an important impact on the material properties, and furthermore it demonstrates the difficulties encountered in trying to establish a general model for the defect chemistry of Bi-containing perovskite systems.
Remark DOI: 10.1007/s10853-016-0186-z
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ID=365

Leaching effect in gadolinia-doped ceria aqueous suspensions for ceramic processes

Authors A. Caldarelli, E. Mercadelli, S. Presto, M. Viviani, A. Sanson
Source
Journal of Power Sources
Volume: 326, Issue: 15, Pages: 70–77
Time of Publication: 2016
Abstract Gadolinium doped ceria (CGO) is a commonly used electrolytic material for Solid Oxide Fuel Cells (SOFCs) and for this reason different shaping methods for its deposition are reported in literature. Most of these processes are based on the use of organic-based CGO suspensions, but water-based processes are acquiring increasingly interest for their economical and environmental friendly properties. In this paper we reported how the components of water-based suspension and some unexpected process parameters can deeply affect the functional properties of the final powder. In particular, we observed that CGO powders are strongly affected by ionic leaching induced by furoic acid used as dispersant: the extent of this leaching was related to the dispersant concentration and suspension’s ball-milling-time; the phenomenon was confirmed by ICP-AES analyses on suspensions surnatant. Most importantly, ionic leaching affected the electrical properties of CGO: leached powder showed a higher ionic conductivity as a consequence of a partial removal of Gd ions at the grain boundaries. This work is therefore pointing out that when considering water-based suspensions, it is extremely important to carefully consider all the process parameters, including the organic components of the ceramic suspension, as these could lead to unexpected effects on the properties of the powder, affecting the performance of the final shaped material.
Keywords Gadolinium doped ceria; Water-based suspensions; Furoic acid; Ionic leaching; Electrical conductivity
Remark doi:10.1016/j.jpowsour.2016.06.069
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ID=360

Electrical characterization of amorphous LiAlO2 thin films deposited by atomic layer deposition

Authors Yang Hu, Amund Ruud, Ville Miikkulainen, Truls Norby, Ola Nilsen and Helmer Fjellvg
Source
RSC Advances
Volume: 6, Issue: 65, Pages: 60479-60486
Time of Publication: 2016
Abstract LiAlO2 thin films deposited by atomic layer deposition (ALD) have a potential application as an electrolyte in three-dimensional (3D) all-solid-state microbatteries. In this study, Li-ion conductivity of such films is investigated by both in-plane and cross-plane methods. LiAlO2 thin films with a Li composition of [Li]/([Li] + [Al]) = 0.46 and an amorphous structure were grown by ALD with thicknesses of 90, 160 and 235 nm on different substrates. The electrical characterization was conducted by impedance spectroscopy using inert electrodes over a temperature range of 25–200 C in an inert atmosphere. In-plane conductivities were obtained from films on insulating sapphire substrates, whereas cross-plane conductivities were measured from films on conducting titanium substrates. For the first time, comparison of the in-plane and cross-plane conductivities in these ALD LiAlO2 films has been achieved. More comparable results are obtained using a cross-plane method, whereas in-plane conductivity measurements demonstrate a considerable thickness-dependence with thinner film thickness. The room-temperature conductivity of the LiAlO2 films has been determined to be in the order of 10−10 S cm−1 with an activation energy of ca. 0.8 eV.
Remark DOI: 10.1039/C6RA03137D
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ID=357

Effect of Nd-deficiency on electrochemical properties of NdBaCo2O6−δ cathode for intermediate-temperature solid oxide fuel cells

Authors Kaihua Yia,Liping Sun, Qiang Li, Tian Xia, Lihua Huo, Hui Zhao, Jingwei Li, Zhe L, Jean-Marc Bassat, Aline Rougier, Sbastien Fourcade, Jean-Claude Grenier
Source
International Journal of Hydrogen Energy
Volume: 41, Issue: 24, Pages: 10228–10238
Time of Publication: 2016
Abstract Nd1−xBaCo2O6−δ (N1−xBCO) is evaluated as cathode materials for intermediate-temperature solid oxide fuel cells (IT-SOFCs). The effects of Nd-deficiency on the crystal structure, thermal expansion behavior, electrical conductivity and electrochemical performance are studied. N1−xBCO oxides crystallize in the orthorhombic symmetry with Pmmm space group. A good chemical compatibility between N1−xBCO and CGO electrolyte is found at 1100 C in air. Introducing Nd-deficiency promotes the formation of oxygen vacancy, and significantly improves the electrochemical performance of N1−xBCO cathodes. The lowest area specific resistance (ASR) value of 0.043 Ω cm2 is obtained on the N0.96BCO cathode at 700 C in air. The rate limiting step for electrochemical oxygen reduction reaction (ORR) is charge transfer process at the interface. The power output of the electrolyte supported cell Ni-CGO/CGO/N0.96BCO reaches 0.6 W cm−2 at 700 C.
Keywords Solid oxide fuel cell; Double perovskite; Nd-deficiency; Cathode; Electrode reaction
Remark doi:10.1016/j.ijhydene.2016.04.248
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ID=356

Controlling mixed conductivity in Na1/2Bi1/2TiO3 using A-site non-stoichiometry and Nb-donor doping

Authors Linhao Li, Ming Li, Huairuo Zhang, Ian M. Reaney and Derek C. Sinclair
Source
J. Mater. Chem. C
Volume: 4, Pages: 5779-5786
Time of Publication: 2016
Abstract Precise control of electronic and/or ionic conductivity in electroceramics is crucial to achieve the desired functional properties as well as to improve manufacturing practices. We recently reported the conventional piezoelectric material Na1/2Bi1/2TiO3 (NBT) can be tuned into a novel oxide-ion conductor with an oxide-ion transport number (tion) > 0.9 by creating bismuth and oxygen vacancies. A small Bi-excess in the nominal starting composition (Na0.50Bi0.50+xTiO3+3x/2, x = 0.01) or Nb-donor doping (Na0.50Bi0.50Ti1−yNbyO3+y/2, 0.005 ≤ y ≤ 0.030) can reduce significantly the electrical conductivity to create dielectric behaviour by filling oxygen vacancies and suppressing oxide ion conduction (tion ≤ 0.10). Here we show a further increase in the starting Bi-excess content (0.02 ≤ x ≤ 0.10) reintroduces significant levels of oxide-ion conductivity and increases tion ∼ 0.4–0.6 to create mixed ionic/electronic behaviour. The switch from insulating to mixed conducting behaviour for x > 0.01 is linked to the presence of Bi-rich secondary phases and we discuss possible explanations for this effect. Mixed conducting behaviour with tion ∼ 0.5–0.6 can also be achieved with lower levels of Nb-doping (y ∼ 0.003) due to incomplete filling of oxygen vacancies without the presence of secondary phases. NBT can now be compositionally tailored to exhibit three types of electrical behaviour; Type I (oxide-ion conductor); Type II (mixed ionic-electronic conductor); Type III (insulator) and these results reveal an approach to fine-tune tion in NBT from near unity to zero. In addition to developing new oxide-ion and now mixed ionic/electronic NBT-based conductors, this flexibility in control of oxygen vacancies allows fine-tuning of both the dielectric/piezoelectric properties and design manufacturing practices for NBT-based multilayer piezoelectric devices.
Remark DOI: 10.1039/C6TC01719C
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ID=355

Influence of cathode functional layer composition on electrochemical performance of solid oxide fuel cells

Authors Antnio de Pdua Lima Fernandes, Eric Marsalha Garcia, Rubens Moreira de Almeida, Hosane Aparecida Taroco, Edyth Priscilla Campos Silva, Rosana Zacarias Domingues, Tulio Matencio
Source
Journal of Solid State Electrochemistry
Time of Publication: 2016
Abstract In this work, anode-supported solid oxide fuel cells (SOFC) were tested with a yttria-stabilized zirconia (YSZ) (8 mol% Y2O3-ZrO2)/gadolinium-doped ceria (GDC) (Ce0.9Gd 0.1O1.95) bilayer electrolyte and two lanthanum strontium cobalt ferrite (LSCF) composition as functional cathode layer: La0.6Sr0.4Co0.8Fe0.2O3-δ (LSCF 1) and La0.60Sr0.40Co0.2Fe0.8O3-δ (LSCF 2). The functional cathode layers were made of 50 % (w/w) LSCF and 50 % (w/w) GDC. Microstructural characterization was performed by scanning electron microscopy and X-ray diffraction. Electrochemical impedance spectroscopy (EIS) and power measurements were performed under oxygen and hydrogen atmospheres. The microscopy studies showed that the LSCF 2 functional layer is more uniform and adherent to the electrolyte and the cathode collector than the LSCF 1 functional layer, which has cracks, chips, and lower adhesion. The use of the LSCF 2 layer allowed an approximately 25-fold reduction in ohmic resistance (0.06 Ω cm−2) compared with the LSCF 1 layer (1.5 Ω cm−2). The power measurements showed a considerable increase in the power cell using LSCF 2 (approximately 420 mW cm−2) compared with the power cell using LSCF 1 (approximately 180 mW cm−2).
Keywords SOFC, LSCF, Interface, Electrochemical performance, Cathode, Functional layer
Remark First Online: 20 May 2016. DOI: 10.1007/s10008-016-3241-4
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ID=352

Direct conversion of methane to aromatics in a catalytic co-ionic membrane reactor

Authors S.H.Morejudo, R.Zanon, S.escolastico, I. Yuste-Tirados, H. Malerd-Fjeld, P.K. Vestre, W.G.Coors, A.Martinez, T.Norby, J.M.Serra, C.Kjlseth
Source
Science
Volume: 353, Issue: 6299, Pages: 563-566
Publisher: American Association for the Advancement of Science (AAAS), ISBN: Print ISSN:0036-8075 Online ISSN:1095-9203, Time of Publication: 2016-08
Abstract Nonoxidative methane dehydroaromatization (MDA: 6CH4 ↔ C6H6 + 9H2) using shape-selective Mo/zeolite catalysts is a key technology for exploitation of stranded natural gas reserves by direct conversion into transportable liquids. However, this reaction faces two major issues: The one-pass conversion is limited by thermodynamics, and the catalyst deactivates quickly through kinetically favored formation of coke. We show that integration of an electrochemical BaZrO3-based membrane exhibiting both proton and oxide ion conductivity into an MDA reactor gives rise to high aromatic yields and improved catalyst stability. These effects originate from the simultaneous extraction of hydrogen and distributed injection of oxide ions along the reactor length. Further, we demonstrate that the electrochemical co-ionic membrane reactor enables high carbon efficiencies (up to 80%) that improve the technoeconomic process viability. Methane gas is expensive to ship. It is usually converted into carbon monoxide and hydrogen and then liquefied. This is economically feasible only on very large scales. Hence, methane produced in small amounts at remote locations is either burned or not extracted. A promising alternative is conversion to benzene and hydrogen with molybdenumzeolite catalysts. Unfortunately, these catalysts deactivate because of carbon buildup; plus, hydrogen has to be removed to drive the reaction forward. Morejudo et al. address both of these problems with a solid-state BaZrO3 membrane reactor that electrochemically removes hydrogen and supplies oxygen to suppress carbon buildup.
Keywords CMR, MDA, catalytic membrane reactor, ZSM-5, MCM-22, FBR, FBR-PolyM, Pd-CMR, Co-ionic CMR, FT, ProboStat CMR base unit (NorECs)
Remark http://science.sciencemag.org/highwire/filestream/682540/field_highwire_adjunct_files/0/Morejudo.SM.pdf
BaZrO3
BaZrO3
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ID=350

Characteristics of Cu and Mo-doped Ca3Co4O9−δ cathode materials for use in solid oxide fuel cells

Authors Sea-Fue Wang, Yung-Fu Hsu, Jing-Han Chang, Soofin Cheng, Hsi-Chuan Lu
Source
Ceramics International
Time of Publication: 2016
Abstract In this study, Cu and Mo ions were doped in Ca3Co4O9−δ to improve the electrical conductivity and electrochemical behavior of Ca3Co4O9−δ ceramic and the performance of a solid oxide fuel cell (SOFC) single cell based on NiO-SDC/SDC/doped Ca3Co4O9−δ-SDC were examined. Cu substitution in the monoclinic Ca3Co4O9−δ ceramic effectively enhanced the densification, slightly increased the grain size, and triggered the formation of some Ca3Co2O6; however, no second phase was found in porous Mo-doped Ca3Co4O9−δ ceramics even when the sintering temperature reached 1050 C. Substitution of Cu ions caused slight increase in the Co3+ and Co4+ contents and decrease in the Co2+ content; however, doping with Mo ions showed the opposite trend. Doping the Ca3Co4O9−δ ceramic with a small amount of Cu or Mo increased its electrical conductivity. The maximum electrical conductivity measured was 218.8 S cm−1 for the Ca3Co3.9Cu0.1O9−δ ceramic at 800 C. The Ca3Co3.9Cu0.1O9−δ ceramic with a coefficient of thermal expansion coefficient of 12.110−6 K−1 was chosen as the cathode to build SOFC single cells consisting of a 20 μm SDC electrolyte layer. Without optimizing the microstructure of the cathode or hermetically sealing the cell against the gas, a power density of 0.367 Wcm−2 at 750 C was achieved, demonstrating that Cu-doped Ca3Co4O9−δ can be used as a potential cathode material for IT-SOFCs.
Keywords Solid oxide fuel cell; Cathode; Impedance; Cell performance
Remark In Press, doi:10.1016/j.ceramint.2016.04.037
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ID=347

Structural study and proton conductivity in BaCe0.7Zr0.25−xYxZn0.05O3 (x = 0.05, 0.1, 0.15, 0.2 & 0.25)

Authors Ahmed Afif, Nikdalila Radenahmad, Chee Ming Lim, Mohamad Iskandar Petra, Md. Aminul Islam, Seikh Mohammad Habibur Rahman, Sten Eriksson, Abul Kalam Azad
Source
International Journal of Hydrogen Energy
Time of Publication: 2016
Abstract Solid oxide fuel cell (SOFC) has been considered to generate power represented by conductivity. Zinc doped Barium Cerium Zirconium Yttrium oxide (BCZYZn) has been found to offer high protonic conductivity and high stability as being electrolyte for proton-conducting SOFCs. In this study, we report a new series of proton conducting materials, BaCe0.7Zr0.25−xYxZn0.05O3 (x = 0.05, 0.1, 0.15, 0.2 and 0.25). The materials were synthesized by solid state reaction route and characterized by X-ray diffraction (XRD), scanning electron microscopy (SEM), thermal expansion, particle size and impedance spectroscopy (IS). Rietveld analysis of the XRD data reveal a cubic perovskite structure with Pm-3m space group up to composition x = 0.15. For x = 0.15 and 0.20, the materials have structural phase change to orthorhombic in the Pbnm space group. Scanning electron microscopy images show high density materials. Thermal expansion measurements show that the thermal expansion coefficient is in the range 10.0–11.0 10−6/C. Impedance spectroscopy shows higher ionic conduction under wet condition compared to dry condition. Y content of 25% (BCZYZn25) exhibits highest conductivity of 1.84 10−2 S/cm in wet Argon. This study indicated that perovskite electrolyte BCZYZn is promising material for the next generation of intermediate temperature solid oxide fuel cells (IT-SOFCs).
Keywords Proton conductor; Sinterability; Rietveld refinement; Conductivity; SOFC electrolyte
Remark In Press, doi:10.1016/j.ijhydene.2016.02.135
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ID=344

Optically-transparent and electrically-conductive AgI–AgPO3–WO3 glass fibers

Authors Maxime Rioux, Yannick Ledemi, Jeff Viens, Steeve Morency, Seyed Alireza Ghaffari and Youns Messaddeq
Source
RSC Advances
Volume: 5, Pages: 40236-40248
Time of Publication: 2015
Abstract In this study, we report to our knowledge the first optically-transparent and electrically-conductive optical glass fiber belonging to the system AgI–AgPO3–WO3. The addition of tungsten oxide (WO3) into the phosphate glassy network allowed the adjustment of the glass transition temperature, thermal expansion coefficient, refractive index, optical band edge, and electrical conductivity, which are all very important parameters in view of drawing glass fibers with a desired set of electrical and optical properties. Furthermore, the addition of WO3 can improve considerably glass stability against water and humidity in the environment. AgI–AgPO3–WO3 glass fibers with 15 mol% WO3 showed 2 dB m−1 optical propagation loss from 800 to 950 nm wavelength range, and 10−3 S cm−1 electrical conductivity at 1 MHz AC frequency. Complex impedance spectra and thermal activation energies ranging from 0.15 to 0.30 eV are indicative of a dominant conductivity mechanism being ionic in nature within the range of AC frequencies from 1 Hz to 1 MHz. Fibers exhibited higher electrical conductivities than the bulk glasses. Glasses in the AgI–AgPO3–WO3 system can be used for fibers that require a set of adjustable properties pertaining to electrical conductivity, optical transparency, and environmental stability.
Remark DOI: 10.1039/C5RA00681C
Link
ID=341

New ferroelastic K2Sr(MoO4)2: Synthesis, phase transitions, crystal and domain structures, ionic conductivity

Authors Galina D. Tsyrenova, Erzhena Т. Pavlova, Sergey F. Solodovnikov, Nadezhda N. Popova, Tatyana Yu. Kardash, Sergey Yu. Stefanovich, Irina А. Gudkova, Zoya A. Solodovnikova, Bogdan I. Lazoryak
Source
Journal of Solid State Chemistry
Volume: 237, Pages: 64–71
Time of Publication: 2016
Abstract K2Sr(MoO4)2 crystals were synthesized and their properties examined. The distortive polymorphic transformations at 421 K (α (LT)→ β(MT)) and 744 K (β(MT)→γ (HT)) of K2Sr(MoO4)2 were studied. It has been shown that the transitions go in sequence from the high-temperature palmierite K2Pb(SO4)2-type γ-phase (R View the MathML source3m) to an intermediate β-phase with a probable incommensurate structure and then to a low-temperature α-phase. Domain structures peculiarities in ferroelastic α-K2Sr(MoO4)2 have been investigated. The electrical conductivity of K2Sr(MoO4)2 rises tenfold in the vicinity of the phase transition at 744 K that may be associated with a change conductivity path from quasi-one-dimensional to two-dimensional. The crystal structure of the α-phase (sp. gr. С2/c, а=14.318(3) , b=5.9337(12) , с=10.422(2) , β=105.83(3), Z=4, R=0.0219) is similar to that of α-Pb3(PO4)2. Sr-atoms are mainly located at site with the coordination number CN=8 (a tetragonal antiprism with bond lengths of 2.578(2)–2.789(2) ) and K atoms are located at site with CN=9+1.
Keywords Potassium; Strontium; molybdates; Phase transitions; Ferroelastics; Crystal structure; Crystal optics analysis; Domain structure; Ionic conductivity
Remark doi:10.1016/j.jssc.2016.01.011
Link
ID=339

Chemical stability and H2 flux degradation of cercer membranes based on lanthanum tungstate and lanthanum chromite

Authors Jonathan M. Polfus, , Zuoan Li, Wen Xing, Martin F. Sunding, John C. Walmsley, Marie-Laure Fontaine, Partow P. Henriksen, Rune Bredesen
Source
Journal of Membrane Science
Volume: 503, Pages: 42–47
Time of Publication: 2016
Abstract Ceramic–ceramic composite (cercer) membranes of (Mo-doped) lanthanum tungstate, La27(W,Mo)5O55.5−δ, and lanthanum chromite, La0.87Sr0.13CrO3−δ, have recently been shown to exhibit H2 permeabilities among state-of-the-art. The present work deals with the long-term stability of these cercer membranes in line with concern of flux degradation and phase instability observed in previous studies. The H2 permeability of disc shaped membranes with varying La/W ratio in the lanthanum tungstate phase (5.35≤La/W≤5.50) was measured at 900 and 1000 C with a feed gas containing 49% H2 and 2.5% H2O for up to 1500 h. It was observed that the H2 permeability decreased by a factor of up to 5.3 over 1500 h at 1000 C. Post-characterization of the membranes and similarly annealed samples was performed by SEM, STEM and XRD, and segregation of La2O3 was observed. The decrease in H2 permeability was ascribed to the compositional instability of the cation-disordered lanthanum tungstate under the measurement conditions. Equilibration of the La/W ratio by segregation of La2O3 leads to a lower ionic conductivity according to the materials inherent defect chemistry. Partial decomposition and reduction of the lanthanum tungstate phase, presumably to metallic tungsten, was also observed after exposure to nominally dry hydrogen.
Keywords Hydrogen separation; Dense ceramic membrane; Ceramic–ceramic composite; Lanthanum tungstate; Lanthanum chromite
Remark doi:10.1016/j.memsci.2015.12.054
Link
ID=335

Experimental and molecular dynamics study of thermo-physical and transport properties of ThO2-5wt.%CeO2 mixed oxides

Authors P.S. Somayajulu, P.S. Ghosh, J. Banerjee, K.L.N.C. Babu, K.M. Danny, B.P. Mandal, T. Mahata, P. Sengupta, S.K. Sali, A. Arya
Source
Journal of Nuclear Materials
Volume: 467, Issue: 2, Pages: 644–659
Time of Publication: 2015
Abstract We have determined the thermo-physical (elastic modulus, specific heat, thermal expansion and thermal conductivity) and transport (ionic conductivity) properties of ThO2-5wt.%CeO2 mixed oxide (MOX) using a combined experimental and theoretical methodology. The specific heat, ionic conductivity and elastic properties of ThO2-5wt.%CeO2 pellets prepared by conventional powder metallurgy (POP) and coated agglomerate pelletization (CAP) routes (sintered in both air and Ar-8%H2 atmosphere) are compared with respect to homogeneity (CeO2 distribution in ThO2 matrix), microstructure, porosity and oxygen to metal ratio. The effects of inhomogeneity and pore distribution on thermal expansion and thermal conductivity of the mixed-oxide pellets are identified. Molecular dynamics (MD) simulations using the Coulomb-Buckingham-Morse-many-body model based interatomic potentials are used to predict elastic properties in the temperature range between 300 and 2000 K and thermodynamic properties, viz., enthalpy increment and specific heats of ThO2. Finally, the thermal expansion coefficient and thermal conductivity of ThO2 and (Th,Ce)O2 mixed-oxides obtained from MD are compared with available experimental results.
Keywords ThO2-5%CeO2 MOX; Specific heat; Ionic conductivity; Temperature dependent elastic properties; Molecular dynamics simulation
Remark doi:10.1016/j.jnucmat.2015.10.053
Link
ID=333

Lithium Polymer Electrolytes Based on Sulfonated Poly(ether ether ketone) for Lithium Polymer Batteries

Authors Savitha Thayumanasundaram, Vijay Shankar Rangasamy, Jin Won Seo andJean-Pierre Locquet
Source
European Journal of Inorganic Chemistry
Volume: 2015, Issue: 32, Pages: 5395–5404
Time of Publication: 2015
Abstract We studied a lithium-ion conducting polymer based on sulfonated poly(ether ether ketone) (SPEEK) doped with lithium bis(trifluoromethane)sulfonimide (LiTFSI). Self-standing membranes were prepared by the solvent-casting technique with a LiTFSI loading of 0 to 30 wt.-%. The thermogravimetric analysis curves showed that the SO3H groups decompose earlier in the SPEEK–LiTFSI membranes than in pure SPEEK, owing to interactions between the Li+ ions and the SO3H groups. X-ray diffraction and differential scanning calorimetry studies showed that the addition of LiTFSI decreased the crystallinity and the glass-transition temperature of the polymer, which revealed the plasticizing effect of the lithium salt on the polymer matrix. The 7Li NMR spectroscopy results showed a single central transition line at around δ = –1.2 ppm, which indicated the presence of free mobile lithium ions. Dynamic mechanical analysis of the membrane showed it to be mechanically stable up to 100 C, a prerequisite for flexible lithium polymer batteries. The highest room-temperature conductivity in the order of 10–5 S cm–1 was observed for the 20 wt.-% LiTFSI-doped SPEEK membrane, which increased to 5  10–4 S cm–1 at 100 C.
Keywords Lithium batteries;Polymer electrolytes;Dynamic mechanical analysis;Raman spectroscopy;Ion pairs
Remark DOI: 10.1002/ejic.201500649
Link
ID=332

Exceptional hydrogen permeation of all-ceramic composite robust membranes based on BaCe0.65Zr0.20Y0.15O3−δ and Y- or Gd-doped ceria

Authors Elena Rebollo, Cecilia Mortal, Sonia Escolstico, Stefano Boldrini, Simona Barison, Jos M. Serra and Monica Fabrizio
Source
Energy Environ. Sci.
Volume: 8, Pages: 3675-3686
Time of Publication: 2015
Abstract Mixed proton and electron conductor ceramic composites were examined as hydrogen separation membranes at moderate temperatures (higher than 500 C). In particular, dense ceramic composites of BaCe0.65Zr0.20Y0.15O3−δ (BCZ20Y15) and Ce0.85M0.15O2−δ (M = Y and Gd, hereafter referred to as YDC15 and GDC15), as protonic and electronic conducting phases respectively, were successfully prepared and tested as hydrogen separation membranes. The mixture of these oxides improved both chemical and mechanical stability and increased the electronic conductivity in dual-phase ceramic membranes. The synthetic method and sintering conditions were optimized to obtain dense and crack free symmetric membranes. The addition of ZnO as a sintering aid allowed achieving robust and dense composites with homogeneous grain distribution. The chemical compatibility between the precursors and the influence of membrane composition on electrical properties and H2 permeability performances were thoroughly investigated. The highest permeation flux was attained for the 50 : 50 volume ratio BCZ20Y15–GDC15 membrane when the feed and the sweep sides of the membrane were hydrated, reaching values of 0.27 mL min−1 cm−2 at 755 C on a 0.65 mm thick membrane sample, currently one of the highest H2 fluxes obtained for bulk mixed protonic–electronic membranes. Increasing the temperature to 1040 C, increased the hydrogen flux up to 2.40 mL min−1 cm−2 when only the sweep side was hydrated. The H2 separation process is attributed to two cooperative mechanisms, i.e. proton transport through the membrane and H2 production via the water splitting reaction coupled with oxygen ion transport. Moreover, these composite systems demonstrated a very good chemical stability under a CO2-rich atmosphere such as catalytic reactors for hydrogen generation.
Remark DOI: 10.1039/C5EE01793A
Link
ID=331

The effect of Cu2O nanoparticle dispersion on the thermoelectric properties of n-type skutterudites

Authors M Battabyal, B Priyadarshini, D Sivaprahasam, N S Karthiselva and R Gopalan
Source
Journal of Physics D: Applied Physics
Volume: 48, Issue: 45 Time of Publication: 2015
Abstract We report the thermoelectric properties of Ba0.4Co4Sb12 and Sn0.4Ba0.4Co4Sb12 skutterudites dispersed with Cu2O nanoparticles. The samples were synthesized by ball milling and consolidated by spark plasma sintering. Dispersion of Cu2O is found to significantly influence the electrical resistivity and thermopower at high temperatures with a more pronounced effect on the electrical resistivity due to the energy filtering effect at the interface between Cu2O nanoparticles and a Ba0.4Co4Sb12 and Sn0.4Ba0.4Co4Sb12 matrix. At 573 K, the electrical resistivity of Ba0.4Co4Sb12 decreases from 5.01    10−5 Ωm to 2.98    10−5 Ωm upon dispersion of Cu2O. The dispersion of Cu2O reduces the thermal conductivity of the samples from 300 K and above by increasing the phonon scattering. The lowest observed thermal conductivity at 573 K is found to be 2.001 W mK−1 in Cu2O dispersed Ba0.4Co4Sb12 while it is 2.91 W mK−1 in the Ba0.4Co4Sb12 sample without Cu2O dispersion. Hence Cu2O dispersion plays a significant role in the thermoelectric properties and a maximum figure of merit (ZT ) ~ 0.92 is achieved in Cu2O dispersed Ba0.4Co4Sb12 at 573 K which is more than 200% compared to the pure Ba0.4Co4Sb12 sample. The results from nanoindentation experiments show that the Cu2O dispersed sample (Cu2O  +  Sn0.4Ba0.4Co4Sb11.6) has a higher reduced Youngs modulus (~139 GPa) than the pure Sn0.4Ba0.4Co4Sb11.6 sample (~128 GPa).
Remark Link
ID=320

Protons in piezoelectric langatate; La3Ga5.5Ta0.5O14

Authors Tor Svendsen Bjrheim, Vijay Shanmugappirabu, Reidar Haugsrud, Truls E. Norby
Source
Solid State Ionics
Volume: 278, Pages: 275–280
Time of Publication: 2015
Abstract This contribution reports the hydration and electrical transport properties of effectively acceptor doped single crystalline and polycrystalline langatate, La3Ga5.5Ta0.5O14. The electrical properties are investigated over wide ranges of pH2OpH2O, pD2OpD2O and pO2pO2 in the temperature range 400 to 1000 C. Acceptor doped langatate is dominated by oxygen vacancies in dry atmospheres and at high temperatures, and by protonic defects in wet atmospheres and at lower temperatures. The corresponding standard hydration enthalpy and entropy are − 90 5 kJ/mol and − 130 5 J/mol K, respectively. Further, all compositions display pure proton conductivity in wet atmospheres below 700 C with a proton mobility enthalpy in the range of 70–75 kJ/mol, depending on doping level and crystallographic direction. Hence, protons are important for the physiochemical properties of langatate even at 1000 C, and could therefore influence the behavior of langatate-based resonator devices. The proton conductivity is slightly anisotropic, being higher in the X- and Y- than in the Z-direction. At high temperatures and under dry conditions, electron holes and oxide ions dominate the conductivity, and the enthalpy of mobility of vacancies is 140 5 kJ/mol.
Keywords Langatate; Piezoelectric; Defects; Protons; Conductivity
Remark doi:10.1016/j.ssi.2015.06.024
Link
ID=319

Tetragonal tungsten bronzes Nb8−xW9+xO47−δ: optimization strategies and transport properties of a new n-type thermoelectric oxide

Authors Christophe P. Heinrich, Matthias Schrade, Giacomo Cerretti, Ingo Lieberwirth, Patrick Leidich, Andreas Schmitz, Harald Fjeld, Eckhard Mueller, Terje G. Finstad, Truls Norby and Wolfgang Tremel
Source
Materials Horizons
Issue: 5, Pages: 519-527
Time of Publication: 2015
Abstract Engineering of nanoscaled structures may help controlling the electrical and thermal transport in solids, in particular for thermoelectric applications that require the combination of low thermal conductivity and low electrical resistivity. The tetragonal tungsten bronzes Nb8−xW9+xO47 (TTB) allow a continuous variation of the charge carrier concentration while fulfilling at the same time the concept of a “phonon-glass electron-crystal” through a layered nanostructure defined by intrinsic crystallographic shear planes. The thermoelectric properties of the tetragonal tungsten bronzes Nb8−xW9+xO47−δ (0 < x < 2) were studied in the temperature range from 373 to 973 K. Structural defects and the thermal stability under various oxygen partial pressure pO2 were investigated by means of thermogravimetry, HR-TEM, and XRD. Nb8W9O47−δ was found stable at 973 K and a pO2 of ≈10−15 atm. The oxygen nonstoichiometry δ can reach up to 0.3, depending on the applied atmosphere. By increasing the substitution level x, the electrical resistivity ρ and the Seebeck coefficient S decreased. For x = 2, ρ reached 20 mΩ cm at 973 K, combined with a Seebeck coefficient of approximately −120 μV K−1. The thermal conductivity was low for all samples, ranging from 1.6 to 2.0 W K−1 m−1, attributed to the complex crystal structure. The best thermoelectric figure of merit zT of the investigated samples was 0.043, obtained for x = 2 at 973 K, but it is expected to increase significantly upon a further increase of x. The control of the oxygen non-stoichiometry δ opens a second independent optimization strategy for tetragonal tungsten bronzes.
Remark DOI: 10.1039/C5MH00033E
Link
ID=315

Gd- and Pr-based double perovskite cobaltites as oxygen electrodes for proton ceramic fuel cells and electrolyser cells

Authors Ragnar Strandbakke, Vladimir A. Cherepanov, Andrey Yu. Zuev, Dmitry S. Tsvetkov, Christos Argirusis, Georgia Sourkouni, Stephan Prnte, Truls Norby
Source
Solid State Ionics
Volume: 278, Pages: 120–132
Time of Publication: 2015
Abstract Double perovskite oxides BaGd0.8La0.2Co2O6−δ (BGLC), BaGdCo1.8Fe0.2O6−δ (BGCF), BaPrCo2O6−δ (BPC) and BaPrCo1.4Fe0.6O6−δ (BPCF) were investigated as oxygen electrodes on mixed conducting BaZr0.7Ce0.2Y0.1O3 (BZCY72) electrolyte using impedance spectroscopy vs temperature, pO2, and pH2O. We propose and have applied a novel approach to extract and parameterise the charge transfer and diffusion impedances of the electrode reactions in a system comprising charge transport of protons, oxide ions, and electrons. Given by the properties of the BZCY72, transport of protons dominates at lower temperatures and high pH2O, oxide ions at higher temperatures, and electron holes increasingly at high temperatures and high pO2. The electrodes showed good performance, with the lowest total apparent polarisation resistance for BGLC/BZCY72 being 0.05 and 10 Ωcm2 at 650 and 350 C, respectively. The low temperature rate limiting reaction step is a surface related process, involving protonic species, with an activation energy of approximately 50 kJ mol−1 for BGLC/BZCY72. The oxide ion transport taking over at higher temperatures exhibits a higher activation energy typical of SOFC cathodes. Thermogravimetric studies revealed that BGLC exhibits considerable protonation at 300–400 C, which may be interpreted as hydration with an enthalpy of approximately –50 kJ mol−1. The resulting mixed proton electron conduction may explain its good performance as electrode on BZCY72.
Keywords PCFC; PCEC; P-MIEC; Proton conductor; Mixed conductivity; Double perovskite
Remark doi:10.1016/j.ssi.2015.05.014
Link
ID=311

Resistivity Enhancement and Transport Mechanisms in (1 − x)BaTiO3–xBi(Zn1/2Ti1/2)O3 and (1 − x)SrTiO3–xBi(Zn1/2Ti1/2)O3

Author Nitish Kumar* andDavid P. Cann
Source
Journal of the American Ceramic Society
Time of Publication: 2015
Abstract Ceramics of composition (1−x)BaTiO3–xBi(Zn1/2Ti1/2)O3 (BT-BZT) were prepared by solid-state synthesis; they have been shown to exhibit excellent properties suited for high-temperature dielectric applications. The X-ray diffraction data showed a single-phase perovskite structure for all the compositions prepared (x ≤ 0.1 BZT). The compositions with less than 0.075 BZT exhibited tetragonal symmetry at room temperature and pseudo-cubic symmetry above it. Most notably, a significant improvement in insulation properties was measured with the addition of BZT. Both low-field AC impedance and high-field direct DC measurements indicated an increase in resistivity of at least two orders of magnitude at 400C with the addition of just 0.03 BZT (~107 Ω-cm) into the solid solution as compared to pure BT (~105 Ω-cm). This effect was also evident in dielectric loss data, which remained low at higher temperatures as the BZT content increased. In conjunction with band gap measurements, it was also concluded that the conduction mechanism transitioned from extrinsic for pure BT to intrinsic for 0.075 BZT suggesting a change in the fundamental defect equilibrium conditions. It was also shown that this improvement in insulation properties was not limited to BT-BZT, but could also be observed in the paraelectric SrTiO3–BZT system.
Remark DOI: 10.1111/jace.13666, Article first published online
Link
ID=306

Crystal structure and high-temperature properties of the Ruddlesden–Popper phases Sr3−xYx(Fe1.25Ni0.75)O7−δ (0≤x≤0.75)

Authors Louise Samain, Philipp Amshoff, Jordi J. Biendicho, Frank Tietz, Abdelfattah Mahmoud, Raphal P. Hermann, Sergey Ya. Istomin, Jekabs Grins, Gunnar Svensson
Source
Journal of Solid State Chemistry
Volume: 227, Pages: 45–54
Time of Publication: 2015
Abstract Ruddlesden–Popper n=2 member phases Sr3−xYxFe1.25Ni0.75O7−δ, 0≤x≤0.75, have been investigated by X-ray and neutron powder diffraction, thermogravimetry and Mssbauer spectroscopy. Both samples as-prepared at 1300 C under N2(g) flow and samples subsequently air-annealed at 900 C were studied. The as-prepared x=0.75 phase is highly oxygen deficient with δ=1, the O1 atom site being vacant, and the Fe3+/Ni2+ ions having a square pyramidal coordination. For as-prepared phases with lower x values, the Mssbauer spectral data are in good agreement with the presence of both 5- and 4-coordinated Fe3+ ions, implying in addition a partial occupancy of the O3 atom sites that form the basal plane of the square pyramid. The air-annealed x=0.75 sample has a δ value of 0.61(1) and the structure has Fe/Ni ions in both square pyramids and octahedra. Mssbauer spectroscopy shows the phase to contain only Fe3+, implying that all Ni is present as Ni3+. Air-annealed phases with lower x values are found to contain both Fe3+ and Fe4+. For both the as-prepared and the air-annealed samples, the Y3+ cations are found to be mainly located in the perovskite block. The high-temperature thermal expansion of as-prepared and air-annealed x=0.75 phases were investigated by high-temperature X-ray diffraction and dilatometry and the linear thermal expansion coefficient determined to be 14.4 ppm K−1. Electrical conductivity measurements showed that the air-annealed samples have higher conductivity than the as-prepared ones.
Keywords Ruddlesden–Popper structure; Oxygen non-stoichiometry; Crystal structure; Mssbauer spectroscopy; Electrical conductivity; Thermal expansion
Remark doi:10.1016/j.jssc.2015.03.018
Link
ID=304

FD Electrolysis: Co-electrolysis of steam and CO2 in full-ceramic symmetrical SOECs: A strategy for avoiding the use of Hydrogen as a safe gas

Authors Marc Torrell, Sergio Garca-Rodrguez, Alex Morata, Germn Penelas and Alberto Tarancon
Source
Faraday Discussions
Time of Publication: 2015
Abstract The use of cermets as fuel electrodes for solid oxide electrolysis cells requires permanent circulation of reducing gas, e.g. H2 or CO, so called safe gas, in order to avoid oxidation of the metallic phase. Replacing metallic based electrodes by pure oxides is therefore proposed as an advantage for the industrial application of solid oxide electrolyzers. In this work, full-ceramic symmetrical solid oxide electrolysis cells have been investigated for steam/CO2 co-electrolysis. Electrolyte supported cells with La0.75Sr0.25Cr0.5Mn0.5O3-δ reversible electrodes have been fabricated and tested in co-electrolysis mode using different fuel compositions, from pure H2O to pure CO2, at temperatures of 850C – 900C. Electrochemical impedance spectroscopy and galvanostatic measurements have been carried out for the mechanistic understanding of the symmetrical cells performance. The content of H2 and CO in the product gas has been measured by in-line gas micro-chromatography. The effect of employing H2 as a safe gas has been also investigated. Maximum density currents of 750 mA/cm2 and 620 mA/cm2 have been applied at 1.7 V for pure H2O and for H2O:CO2 ratios of 1:1, respectively. Remarkable results were obtained for hydrogen-free fuel compositions, which confirmed the interest of using ceramic oxides as a fuel electrode candidate to reduce or completely avoid the use of safe gas in operation minimizing the contribution of the reverse water shift reaction (RWSR) in the process. H2:CO ratios close to two were obtained for hydrogen-free tests fulfilling the basic requirements for synthetic fuel production. An important increase of the operation voltage was detected under continuous operation leading to a dramatic failure by delamination of the oxygen electrode.
Remark Accepted Manuscript, DOI: 10.1039/C5FD00018A
Link
ID=303

Doping strategies for increased oxygen permeability of CaTiO3 based membranes

Authors Jonathan M. Polfus, Wen Xing, Martin F. Sunding, Sidsel M. Hanetho, Paul Inge Dahl, Yngve Larring, Marie-Laure Fontaine, Rune Bredesen
Source
Journal of Membrane Science
Volume: 482, Pages: 137–143
Time of Publication: 2015
Abstract Oxygen permeation measurements are performed on dense samples of CaTi0.85Fe0.15O3−δ, CaTi0.75Fe0.15Mg0.05O3−δ and CaTi0.75Fe0.15Mn0.10O3−δ in combination with density functional theory (DFT) calculations and X-ray photoelectron spectroscopy (XPS) in order to assess Mg and Mn as dopants for improving the O2 permeability of CaTi1−xFexO3−δ based oxygen separation membranes. The oxygen permeation measurements were carried out at temperatures ranging between 700 and 1000 C with feed side oxygen partial pressures between 0.01 and 1 bar. The O2 permeability was experimentally found to be highest for the Mn doped sample over the whole temperature range, reaching 4.210−3 ml min−1 cm−1 at 900 C and 0.21 bar O2 in the feed which corresponds to a 40% increase over the Fe-doped sample and similar to reported values for x=0.2. While the O2 permeability of the Mg doped sample was also higher than the Fe-doped sample, it approached that of the Fe-doped sample above 900 C. According to the DFT calculations, Mn introduces electronic states within the band gap and will predominately exist in the effectively negative charge state, as indicated by XPS measurements. Mn may therefore improve the ionic and electronic conductivity of CTF based membranes. The results are discussed in terms of the limiting species for ambipolar transport and O2 permeability, i.e., oxygen vacancies and electronic charge carriers.
Keywords Dense ceramic oxygen membrane; Ambipolar transport; Mixed ionic-electronic conduction; CaTiO3; Calcium titanate
Remark doi:10.1016/j.memsci.2015.02.036
Link
ID=300

Electrical conductivity and thermopower of (1 − x) BiFeO3 – xBi0.5K0.5TiO3 (x = 0.1, 0.2) ceramics near the ferroelectric to paraelectric phase transition

Authors E. T. Wefring, M.-A. Einarsrud and T. Grande
Source
Physical Chemistry Chemical Physics
Volume: 17, Issue: 14, Pages: 9420-9428
Time of Publication: 2015
Abstract Ferroelectric BiFeO3 has attractive properties such as high strain and polarization, but a wide range of applications of bulk BiFeO3 are hindered due to high leakage currents and a high coercive electric field. Here, we report on the thermal behaviour of the electrical conductivity and thermopower of BiFeO3 substituted with 10 and 20 mol% Bi0.5K0.5TiO3. A change from p-type to n-type conductivity in these semi-conducting materials was demonstrated by the change in the sign of the Seebeck coefficient and the change in the slope of the isothermal conductivity versus partial pressure of O. A minimum in the isothermal conductivity was observed at [similar]10−2 bar O2 partial pressure for both solid solutions. The strong dependence of the conductivity on the partial pressure of O2 was rationalized by a point defect model describing qualitatively the conductivity involving oxidation/reduction of Fe3+, the dominating oxidation state of Fe in stoichiometric BiFeO3. The ferroelectric to paraelectric phase transition of 80 and 90 mol% BiFeO3 was observed at 648 15 and 723 15 C respectively by differential thermal analysis and confirmed by dielectric spectroscopy and high temperature powder X-ray diffraction.
Remark DOI: 10.1039/C5CP00266D
Link
ID=294

Hydrogen separation membranes based on dense ceramic composites in the La27W5O55.5–LaCrO3 system

Authors Jonathan M. Polfus, Wen Xing, Marie-Laure Fontaine, Christelle Denonville, Partow P. Henriksen, Rune Bredesen
Source
Journal of Membrane Science
Volume: 479, Pages: 39–45
Time of Publication: 2015
Abstract Some compositions of ceramic hydrogen permeable membranes are promising for integration in high temperature processes such as steam methane reforming due to their high chemical stability in large chemical gradients and CO2 containing atmospheres. In the present work, we investigate the hydrogen permeability of densely sintered ceramic composites (cercer) of two mixed ionic-electronic conductors: La27W3.5Mo1.5O55.5−δ (LWM) containing 30, 40 and 50 wt% La0.87Sr0.13CrO3−δ (LSC). Hydrogen permeation was characterized as a function of temperature, feed side hydrogen partial pressure (0.1–0.9 bar) with wet and dry sweep gas. In order to assess potentially limiting surface kinetics, measurements were also carried out after applying a catalytic Pt-coating to the feed and sweep side surfaces. The apparent hydrogen permeability, with contribution from both H2 permeation and water splitting on the sweep side, was highest for LWM70-LSC30 with both wet and dry sweep gas. The Pt-coating further enhances the apparent H2 permeability, particularly at lower temperatures. The apparent H2 permeability at 700 C in wet 50% H2 was 1.110−3 mL min−1 cm−1 with wet sweep gas, which is higher than for the pure LWM material. The present work demonstrates that designing dual-phase ceramic composites of mixed ionic-electronic conductors is a promising strategy for enhancing the ambipolar conductivity and gas permeability of dense ceramic membranes.
Keywords Hydrogen separation; Dense ceramic membrane; Ceramic–ceramic composite; Lanthanum tungstate; Lanthanum chromite
Remark doi:10.1016/j.memsci.2015.01.027
Link
ID=293

Bi1−xNbxO1.5+x (x=0.0625, 0.12) fast ion conductors: Structures, stability and oxide ion migration pathways

Authors Matthew L. Tate, Jennifer Hack, Xiaojun Kuang, Garry J. McIntyre, Ray L. Withers, Mark R. Johnson, Ivana Radosavljevic Evans
Source
Journal of Solid State Chemistry
Volume: 225, Pages: 383–390
Time of Publication: 2015
Abstract A combined experimental and computational study of Bi1−xNbxO1.5+x (x=0.0625 and 0.12) has been carried out using laboratory X-ray, neutron and electron diffraction, impedance measurements and ab-initio molecular dynamics. We demonstrate that Bi0.9375Nb0.0625O1.5625, previously reported to adopt a cubic fluorite-type superstructure, can form two different polymorphs depending on the synthetic method: a metastable cubic phase is produced by quenching; while slower cooling yields a stable material with a tetragonal √2√21 superstructure, which undergoes a reversible phase transition into the cubic form at ~680 C on subsequent reheating. Neutron diffraction reveals that the tetragonal superstructure arises mainly from ordering in the oxygen sublattice, with Bi and Nb remaining disordered, although structured diffuse scattering observed in the electron diffraction patterns suggests a degree of short-range ordering. Both materials are oxide ion conductors. On thermal cycling, Bi0.88Nb0.12O1.62 exhibits a decrease in conductivity of approximately an order of magnitude due to partial transformation into the tetragonal phase, but still exhibits conductivity comparable to yttria-stabilised zirconia (YSZ). Ab-initio molecular dynamics simulations performed on Bi0.9375Nb0.0625O1.5625 show that oxide ion diffusion occurs by O2− jumps between edge- and corner-sharing OM4 groups (M=Bi, Nb) via tetrahedral □M4 and octahedral □M6 vacancies.
Keywords Functional oxides; Fast ion conductors; Complex superstructures
Remark doi:10.1016/j.jssc.2015.01.006
Link
ID=292

Functional properties of La0.99X0.01Nb0.99Al0.01O4−δ and La0.99X0.01Nb0.99Ti0.01O4−δ proton conductors where X is an alkaline earth cation

Authors Mariya E. Ivanova, Wilhelm A. Meulenberg, Justinas Palisaitis, Doris Sebold, Cecilia Sols, Mirko Ziegner, Jose M. Serra, Joachim Mayer, Michael Hnsel, Olivier Guillon
Source
Journal of the European Ceramic Society
Volume: 35, Issue: 4, Pages: 1239–1253
Time of Publication: 2015
Abstract Lanthanum niobates with general formulas of La0.99X0.01Nb0.99Al0.01O4−δ and La0.99X0.01Nb0.99Ti0.01O4−δ (X = Mg, Ca, Sr or Ba) were synthesized via the conventional solid state reaction. Specimens with relative density above 96% were produced after sintering. Structural and phase composition studies revealed predominant monoclinic Fergusonite structure for the majority of samples. SEM and TEM studies elucidated the effect of the used dopant combinations on grain growth, micro-crack formation and secondary phase formation. Results from microstructural study were correlated to the grain interior and grain boundary conductivities for selected samples (La0.99Sr0.01Nb0.99Al0.01O4−δ and La0.99Sr0.01Nb0.99Ti0.01O4−δ). The majority of co-doped niobates exhibited appreciable protonic conductivity under humid atmospheres at intermediate temperatures. Sr- or Ca-doped compounds displayed the highest total conductivities with values for LSNA equal to 6 10−4 S/cm and 3 10−4 S/cm in wet air and in wet 4% H2–Ar (900 C), respectively. Additionally, thermal expansion was studied to complete functional characterization of co-doped LaNbO4.
Keywords Proton-conducting ceramic materials; Hydrogen transport ceramic membranes; Rare earth ortho-niobates; Acceptor-doped lanthanum niobates
Remark doi:10.1016/j.jeurceramsoc.2014.11.009
Link
ID=290

Savitha Thayumanasundaram, Vijay Shankar Rangasamy, Niels De Greef, Jin Won Seo andJean-Pierre Locquet

Author Hybrid Polymer Electrolytes Based on a Poly(vinyl alcohol)/Poly(acrylic acid) Blend and a Pyrrolidinium-Based Ionic Liquid for Lithium-Ion Batteries
Source
European Journal of Inorganic Chemistry
Volume: 2015, Issue: 7, Pages: 1290–1299
Time of Publication: 2014
Abstract Polymer blends of poly(vinyl alcohol) (PVA) and poly(acrylic acid) (PAA) were prepared with different molar ratios by a solvent-casting technique. The XRD patterns of the blends show that the degree of crystallinity of the PVA membranes decreases with the addition of PAA owing to the formation of interpenetrating polymer chains. The vibrational spectra of the blend membranes reveal the formation of strong hydrogen bonding between PVA and PAA. Dynamic mechanical analysis (DMA) reveals that the storage modulus of a 25 mol-% PAA sample is comparable to that of pure PVA and, therefore, confirms the mechanical stability of the blend membranes. Significant changes in the peak areas and chemical shifts of the PVA hydroxyl signal (δ = 4–5 ppm) in the 1H NMR spectra of the blend membranes confirm the strong hydrogen bonding between the OH groups of PVA and PAA. The ionic liquid (IL) 1-butyl-1-methylpyrrolidinium bis(trifluoromethanesulfonyl)imide (PYR14TFSI) with 0.2 M lithium bis(trifluoromethanesulfonyl)imide (LiTFSI) was added to the polymer blend to prepare flexible, nonvolatile hybrid polymer electrolytes for lithium-ion batteries. A maximum ionic conductivity of 1 mS cm–1 is observed at 90 C for the membrane with 70 mol-% IL.
Keywords Polymers;Ionic liquids;Hybrid membranes;Hydrogen bonds;Lithium batteries
Remark DOI: 10.1002/ejic.201402603
Link
ID=286

Functional properties of La0.99X0.01Nb0.99Al0.01O4−δ and La0.99X0.01Nb0.99Ti0.01O4−δ proton conductors where X is an alkaline earth cation

Authors Mariya E. Ivanovaa, Wilhelm A. Meulenberga, Justinas Palisaitisb, Doris Sebolda, Cecilia Solsd, Mirko Ziegnere, Jose M. Serrad, Joachim Mayerb, Michael Hnsele, Olivier Guillona
Source
Journal of the European Ceramic Society
Time of Publication: 2014-12
Abstract Lanthanum niobates with general formulas of La0.99X0.01Nb0.99Al0.01O4−δ and La0.99X0.01Nb0.99Ti0.01O4−δ (X = Mg, Ca, Sr or Ba) were synthesized via the conventional solid state reaction. Specimens with relative density above 96% were produced after sintering. Structural and phase composition studies revealed predominant monoclinic Fergusonite structure for the majority of samples. SEM and TEM studies elucidated the effect of the used dopant combinations on grain growth, micro-crack formation and secondary phase formation. Results from microstructural study were correlated to the grain interior and grain boundary conductivities for selected samples (La0.99Sr0.01Nb0.99Al0.01O4−δ and La0.99Sr0.01Nb0.99Ti0.01O4−δ). The majority of co-doped niobates exhibited appreciable protonic conductivity under humid atmospheres at intermediate temperatures. Sr- or Ca-doped compounds displayed the highest total conductivities with values for LSNA equal to 6 10−4 S/cm and 3 10−4 S/cm in wet air and in wet 4% H2–Ar (900 C), respectively. Additionally, thermal expansion was studied to complete functional characterization of co-doped LaNbO4.
Keywords Proton-conducting ceramic materials, Hydrogen transport ceramic membranes, Rare earth ortho-niobates, Acceptor-doped lanthanum niobates, ProGasMix
Remark Link
ID=284

Electrochemical behavior of the pyrochlore- and fluorite-like solid solutions in the Pr2O3–ZrO2 system. Part I

Authors D.A. Belov, A.V. Shlyakhtina, J.C.C. Abrantes, S.A. Chernyak, G.A. Gasymova, O.K. Karyagina, L.G. Shcherbakova
Source
Solid State Ionics
Time of Publication: 2014
Abstract We have studied the structure, microstructure, and electrochemical properties in air of (Pr2 − xZrx)Zr2O7 + x/2 (x = 0.15, 0.32, 0.78), Pr2Zr2O7, and Pr2(Zr2 − xPrx)O7 − x/2 (x = 0.1, 0.4, 1) materials. The solid solutions were prepared through coprecipitation followed by heat treatment of the precursors at 1550 C for 4 h. According to XRD data, the extent of the pyrochlore-like Pr2 xZr2 xO7 x/2 solid solutions at 1550 C is ~ 6 mol.%, which is considerably smaller than that in the NdZrO and SmZrO systems at this temperature. Among the pyrochlores, the highest bulk conductivity was offered by the (Pr2 − xZrx)Zr2O7 + x/2 (x = 0.15): 7.15 10− 3 S/cm at 800 C (Ea = 0.66 eV). The pyrochlore-like Pr2(Zr2 − xPrx)O7 − x/2 (x = 0.1) had lower conductivity (3.97 10− 3 S/cm at 800 C). The highest bulk conductivity among the materials studied was found in the Pr2O3-rich fluorite-like Pr2(Zr2 − xPrx)O7 − x/2 with x = 1: ~ 0.217 S/cm at 800 C (Ea = 0.0.31 eV). The temperature-dependent conductivity of the Pr2O3-rich fluorite-like solid solutions Pr2(Zr2 − xPrx)O7 − x/2 with x = 0.4 and 1 had a break at 560 C, suggesting a change in the mechanism of ion transport at this temperature.
Remark DOI: 10.1016/j.ssi.2014.09.035
Link
ID=281

Structural and electrical study of samarium doped cerium oxide thin films prepared by e-beam evaporation

Authors Darius Virbukas, Mantas Sriubas, Giedrius Laukaitis
Source
Solid State Ionics
Time of Publication: 2014
Abstract Samarium doped cerium oxide (Sm0.15Ce0.85O1.925, SDC) thin films were grown on the Alloy 600 (Fe–Ni–Cr) and optical quartz (SiO2) substrates using e-beam deposition technique. Formed SDC thin films were characterized using different X-ray diffraction (XRD) techniques, scanning electron microscope (SEM), energy-dispersive spectrometry (EDS) and impedance spectroscopy. The deposition rate of formed SDC thin films was changed from 2 /s to 16 /s. XRD analysis shows that all thin films have a cubic (FCC) structure and repeat the crystallographic orientation of the initial powders evaporated with different deposition rate and on different substrates. The crystallite size increases from 7.7 nm to 10.3 nm and from 7.2 nm to 9.2 nm on Alloy 600 substrate and optical quartz (SiO2) substrate respectively as the thin film deposition rate increases. SEM images indicate a dense and homogeneous structure of all formed SDC thin films. The ionic conductivity depends on thin films density and blocking factor. The best ionic conductivity (σg = 1.34 Sm− 1 and σgb = 2.29 Sm −1 at 873 K temperature, activation energy ΔEg = 0.91 eV and ΔEgb = 0.99 eV) was achieved for SDC thin films formed at 4 /s deposition rate. It was found that the highest density (5.25 g/cm3) and the lowest relaxation time in grain (τg = 9.83 10− 7 s), and the lowest blocking factor (0.39) is in SDC thin films formed at 4 /s deposition rate. The deposition rate influences the stoichiometry of the formed SDC thin ceramic films.
Keywords Electron beam deposition; Samarium doped ceria oxide (SDC); Solid oxide fuel cells (SOFC); Ionic conductivity
Remark DOI: 10.1016/j.ssi.2014.09.036
Link
ID=279

Synthesis, crystal structure and properties of alluaudite-like triple molybdate Na25Cs8Fe5(MoO4)24

Authors Aleksandra A. Savina, Sergey F. Solodovnikov, Dmitry A. Belov, Olga M. Basovich, Zoya A. Solodovnikova, Konstantin V. Pokholok, Sergey Yu. Stefanovich, Bogdan I. Lazoryak, Elena G. Khaikina
Source
Journal of Solid State Chemistry
Volume: 220, Pages: 217–220
Time of Publication: 2014
Abstract A new triple molybdate Na25Cs8Fe5(MoO4)24 was synthesized using solid state reactions and studied with X-ray powder diffraction, second harmonic generation (SHG) technique, differential scanning calorimetry, Mssbauer and dielectric impedance spectroscopy. Single crystals of Na25Cs8Fe5(MoO4)24 were obtained and its structure was solved (the space group P View the MathML source1, a=12.5814(5), b=13.8989(5), c=28.4386(9) , α=90.108(2), β=90.064(2), γ=90.020(2), V=4973.0(3) 3, Z=2, R=0.0440). Characteristic features of the structure are polyhedral layers composed of pairs of edge-shared FeO6 and (Fe, Na)O6 octahedra, which are connected by bridging МоО4 tetrahedra. The layers share common vertices with bridging МоО4 tetrahedra to form an open 3D framework with the cavities occupied by the Cs+ and Na+ cations. The compound undergoes first-order phase transformation at 642 K and above this phase transition, electrical conductivity reaches 10−3–10−2 S cm−1. Thus, Na25Cs8Fe5(MoO4)24 may be considered as a promising compound for developing new materials with high ionic conductivity.
Keywords Triple molybdate; Sodium; Synthesis; Crystal structure; Phase transition; Ionic conductivity
Remark DOI: 10.1016/j.jssc.2014.09.004
Link
ID=277

Superior electrochemical performance and oxygen reduction kinetics of layered perovskite PrBaxCo2O5+δ (x = 0.90–1.0) oxides as cathode materials for intermediate-temperature solid oxide fuel cells

Authors Jingping Wang, Fuchang Meng, Tian Xia, Zhan Shi, Jie Lian, Chunbo Xu, Hui Zhao, Jean-Marc Bassat, Jean-Claude Grenier
Source
International Journal of Hydrogen Energy
Time of Publication: 2014
Abstract The layered perovskite PrBaxCo2O5+δ (PBxCO, x = 0.90–1.0) oxides have been synthesized by a solid-state reaction technique, and evaluated as the potential cathode materials for intermediate-temperature solid oxide fuel cells (IT-SOFCs). Room temperature X-ray diffraction patterns show the orthorhombic structures which double the lattice parameters from the perovskite cell parameter as a ≈ ap, b ≈ ap and c ≈ 2ap (ap is the cell parameter of the primitive perovskite) in the Pmmm space group. There is a good chemical compatibility between the PBxCO cathode and the Ce0.9Gd0.1O1.95 (CGO) electrolyte at 1000 C. The electrical conductivity and thermal expansion coefficient of PBxCO are improved due to the increased amount of electronic holes originated from the Ba-deficiency. The results demonstrate the high electrochemical performance of PBxCO cathodes, as evidenced by the super low polarization resistances (Rp) over the intermediate temperature range. The lowest Rp value, 0.042 Ω cm2, and the cathodic overpotential, −15 mV at a current density of −25 mA cm−2, are obtained in the PrBa0.94Co2O5+δ cathode at 600 C in air, which thus allow to be used as a highly promising cathode for IT-SOFCs. A CGO electrolyte fuel cell with the PrBa0.94Co2O5+δ cathode presents the attractive peak power density of ∼1.0 W cm−2 at 700 C. Furthermore, the oxygen reduction kinetics of the PrBa0.94Co2O5+δ cathode is also studied, and the rate-limiting steps for oxygen reduction reaction are determined at different temperatures.
Remark DOI: 10.1016/j.ijhydene.2014.09.041
Link
ID=276

Organic–Inorganic Hybrid Membranes Based on Sulfonated Poly(ether ether ketone) and Tetrabutylphosphonium Bromide Ionic Liquid for PEM Fuel Cell Applications

Authors Vijay Shankar Rangasamy, Savitha Thayumanasundaram, Niels de Greef, Jin Won Seo and Jean-Pierre Locquet
Source
European Journal of Inorganic Chemistry
Time of Publication: 2014
Abstract Ionic liquids (ILs), with their inherent ionic conductivity and negligible vapor pressure, can be exploited in proton exchange membrane (PEM) fuel cells for which thermal management is a major problem and the cell operation temperature is limited by the boiling point of water. In this work, sulfonated poly(ether ether ketone) (SPEEK) membranes were modified by the incorporation of tetrabutylphosphonium bromide ([P4 4 4 4]Br) by solvent-casting. Electrochemical impedance spectroscopy (EIS) was used to study the electrical properties of the modified membranes. Simultaneous TGA and FTIR studies were used to evaluate the thermal stability and chemical structure of the modified membranes, respectively. 1H NMR spectroscopy was applied to probe the changes in the chemical environment due to the interaction between the ionic liquid and the polymer. Mechanical properties were studied by dynamic mechanical analysis. The temperature-dependent behavior of the viscosity of the [P4 4 4 4]Br ionic liquid was observed to obey the Vogel–Fulcher–Tammann (VFT) equation, and was correlated to the ion-conducting properties of the IL-doped SPEEK membranes.
Remark DOI: 10.1002/ejic.201402558
Link
ID=270

Conductivity and oxygen reduction activity changes in lanthanum strontium manganite upon low-level chromium substitution

Authors George Tsekouras, Artur Braun
Source
Solid State Ionics
Volume: 266, Pages: 19-24
Time of Publication: 2014
Abstract On the timescale of solid oxide fuel cell (SOFC) system lifetime requirements, the thermodynamically predicted low-level substitution of chromium on the B-site of (La,Sr)MnO3 could be a source of cathode degradation underlying more overt and well-known chromium poisoning mechanisms. To study this phenomenon in isolation, electronic conductivity (σ) and electrochemical oxygen reduction activity of the (La0.8Sr0.2)0.98CrxMn1−xO3 model series (x = 0, 0.02, 0.05 or 0.1) were measured in air between 850 and 650 C. Depending on the extent of chromium substitution and the measurement temperature, electrochemical impedance spectroscopy (EIS) results could be deconvoluted into a maximum of three contributions reflecting possible limiting processes such as oxide ion transport and dissociative adsorption. Chromium substitution resulted in lowered σ (from 174 S cm− 1 (x = 0) to 89 S cm− 1 (x = 0.1) at 850 C) and a steady rise in associated activation energy (Ea) (from 0.105 0.001 eV (x = 0) to 0.139 0.001 eV (x = 0.1)). From EIS analyses, ohmic and polarisation resistances increased, whilst Ea for the overall oxygen reduction reaction also increased from 1.39 0.04 eV (x = 0) to 1.48–1.54 0.04 eV upon chromium substitution.
Keywords Solid oxide fuel cell; Lanthanum strontium manganite; Chromium poisoning; Electronic conductivity; Electrochemical impedance spectroscopy
Remark Link
ID=269

The effect of calcination temperature on the electrochemical properties of La0.3Sr0.7Fe0.7Cr0.3O3−x (LSFC) perovskite oxide anode of solid oxide fuel cells (SOFCs)

Authors Yifei Sun, Ning Yan, Jianhui Li, Huayi Wu, Jing-Li Luo, Karl T. Chuang
Source
Sustainable Energy Technologies and Assessments
Volume: 8, Pages: 92-98
Time of Publication: 2014
Abstract A series of perovskite structure anode materials, LSFC, was successfully prepared by a glycine combustion process and further calcined at different temperatures. The electrochemical properties of anodes prepared at various calcination temperatures (1100 C, 1200 C and 1300 C) were investigated. The calcination temperature had no significant influence on the morphology of the material but showed obvious influences on the particle sizes and electrochemical properties of the materials. Higher calcination temperature results in sharper X-ray diffractometer (XRD) diffraction peaks of the materials with larger particle sizes and higher electrical conductivity. However materials calcined at higher temperature had much smaller BET surface area resulting in lower triple phase boundary (TPB). The electrochemical performance test exhibited that LSFC anode material sintered at 1100 C exhibited the smallest area specific resistance (ASR) value in H2 at operating temperatures from 700 to 900 C. For proton conducting SOFCs (PC-SOFCs) fed by syngas, the cell with anode calcined at 1100 C also showed highest power density output of 120 mW/cm2 at 750 C, which was almost three times higher than that of the cell with anode calcined at 1300 C.
Keywords Solid oxide fuel cell; Calcination temperature; Electrochemical properties; Perovskite
Remark Link
ID=267

MICROWAVE SINTERING OF Sr AND Mg-DOPED LANTHANUM GALLATE (LSGM) SOLID ELECTROLYTES

Authors Cristian Andronescu, Victor Fruth, Enikoe Volceanov, Rares Scurtu, Cornel Munteanu, Maria Zaharescu
Source
Romanian journal of materials
Time of Publication: 2014-01
Abstract Sr2+ and Mg2+ simultaneously doped lanthanum gallate (LSGM) powders, prepared by a modified Pechini route using polyvinyl alcohol (PVA) as polymeric alcohol, were densified using an activated microwave technique at 2.45 GHz, to develop a dense stable electrolyte for application in intermediate temperatures solid oxide fuel cells (IT-SOFC). Thermal behaviour of precursors was investigated by means of differential thermal analysis combined with thermogravimetric analysis (DTA/TGA). The powders and sintered samples were characterized using scanning electron microscopy and energy dispersive analysis (SEM-EDAX), X-ray diffraction (XRD) and infrared spectroscopy (FT-IR). The thermal expansion coefficient (TEC) and ionic conductivity of the sintered samples were also evaluated. Fine, homogeneous and high density pellets of almost pure LSGM phase were obtained after sintering at 14000C for a short period time in an activated microwave field. Using activated microwave field, due to the volumetric in situ heating, the sintering process is highly specific and instantaneous, leading to a faster kinetics compared to the conventional process (electric oven). With an optimized sintering schedule, a fine grained and dense microstructure of the samples were obtained.
Remark Link
ID=265

Full ceramic micro solid oxide fuel cells: towards more reliable MEMS power generators operating at high temperatures

Authors I. Garbayo, D. Pla, A. Morata, L. Fonseca, N. Sabat and A. Tarancn
Source
Energy Environ. Sci.
Time of Publication: 2014
Abstract Batteries, with a limited capacity, have dominated the power supply of portable devices for decades. Recently, the emergence of new types of highly efficient miniaturized power generators like micro fuel cells has opened up alternatives for continuous operation on the basis of unlimited fuel feeding. This work addresses for the first time the development of a full ceramic micro solid oxide fuel cell fabricated in silicon technology. This full-ceramic device represents a new generation of miniaturized power generators able to operate at high temperatures, and therefore able to work with a hydrocarbon fuel supply. Dense yttria-stabilized zirconia free-standing large-area membranes on micromachined silicon were used as the electrolyte. Thin-film porous electrodes of La0.6Sr0.4CoO3−δ and gadolinia-doped ceria were employed as cathode and anode materials, respectively. The electrochemical performance of all the components was evaluated by partial characterization using symmetrical cells, yielding excellent performance for the electrolyte (area specific resistance of 0.15 Ω cm2 at temperatures as low as 450 C) and the electrodes (area specific resistance of the cathode and anode below 0.3 Ω cm2 at 700 C). A micro solid oxide fuel cell with an active area of 2 mm2 and less than 1 micrometer in thickness was characterized under fuel cell conditions, using hydrogen as a fuel and air as an oxidant. A maximum power density of 100 mW cm−2 and 2 mW per single membrane was generated at 750 C, having an open circuit voltage of 1.05 V. Impedance spectroscopy of the all-ceramic membrane showed a total area-specific resistance of [similar]3.5 Ω cm2.
Remark DOI: 10.1039/C4EE00748D
Link
ID=264

Proton conductivity of hexagonal and cubic BaTi1−xScxO3−δ (0.1 ≤ x ≤ 0.8)

Authors Seikh M. H. Rahman, Stefan T. Norberg, Christopher S. Knee, Jordi J. Biendicho, Stephen Hull and Sten G. Eriksson
Source
Dalton Transactions
Time of Publication: 2014
Abstract BaTi1−xScxO3−δ (x = 0.1–0.8) was prepared via solid state reaction. High resolution X-ray powder diffraction was used to characterise the synthesised materials. It was found that low substitution (x = 0.1 and 0.2) of Ti4+ for Sc3+ gives a hexagonal perovskite structure, whereas high substitution (x = 0.5–0.7) results in a cubic perovskite structure. Thermogravimetric analysis revealed significant levels of protons in both as-prepared and hydrated samples. Electrical conductivity was measured by AC impedance methods under oxygen, argon and under dry and humid, both H2O and D2O, conditions for BaTi1−xScxO3−δ (x = 0.2, 0.6 and 0.7). In the temperature range of 150–600 C, under humid conditions, the conductivity is significantly higher than that under the dry conditions. The increase in conductivity is especially prominent for the cubic phases, indicating that protons are the dominant charge carriers. The proton conductivity of hexagonal BaTi0.8Sc0.2O3−δ is approx. two orders of magnitude lower than that of the more heavily substituted cubic phases. Conductivity is also found to be higher in dry O2 than in Ar in the whole temperature range of 150–1000 C, characteristic of a significant contribution from p-type charge carriers under oxidising atmospheres. Greater Sc3+ substitution leads to a higher proton concentration and the highest proton conductivity (σ [similar] 2 10−3 S cm−1 at 600 C) is found for the BaTi0.3Sc0.7O3−δ composition.
Remark DOI: 10.1039/C4DT01280A
Link
ID=257

Hydrogen permeation characteristics of La27Mo1.5W3.5O55.5

Authors Einar Vllestad, Camilla K. Vigen, Anna Magras, Reidar Haugsrud
Source
Journal of Membrane Science
Volume: 461, Pages: 81–88
Time of Publication: 2014
Abstract Hydrogen permeation in 30% Mo-substituted lanthanum tungsten oxide membranes, La27Mo1.5W3.5O55.5 (LWMo), has been measured as a function of temperature, hydrogen partial pressure gradient, and water vapor pressure in the sweep gas. Transport of hydrogen by means of ambipolar proton–electron conductivity and – with wet sweep gas – water splitting contributes to the measured hydrogen content in the permeate. At 700 C under dry sweep conditions, the H2 permeability in LWMo was 610−4610−4 mL min−1 cm-1, which is significantly higher than that for state-of-the-art SrCeO3-based membranes. Proton conductivity was identified as rate limiting for ambipolar bulk transport across the membrane. On these bases it is evident that Mo-substitution is a successful doping strategy to increase the n-type conductivity and H2 permeability compared to nominally unsubstituted lanthanum tungsten oxide. A steady-state model based on the Wagner transport theory with partial conductivities as input parameters predicted H2 permeabilities in good agreement with the measured data. LWMo is a highly competitive mixed proton–electron conducting oxide for hydrogen transport membrane applications provided that long term stability can be ensured.
Remark http://dx.doi.org/10.1016/j.memsci.2014.03.011
Link
ID=255

Oxide ion transport in (Nd2−xZrx)Zr2O7+δ electrolytes by an interstitial mechanism

Authors A.V. Shlyakhtina, D.A. Belov, A.V. Knotko, M. Avdeev, I.V. Kolbanev, G.A. Vorobieva, O.K. Karyagina, L.G. Shcherbakova
Source
Journal of Alloys and Compounds
Volume: 603, Issue: 5, Pages: 274–281
Time of Publication: 2014
Abstract We have studied the structure and transport properties of ten (Nd2−xZrx)Zr2O7+x/2 (x = 0–1.27) solid solutions, which lie in the ZrO2–Nd2Zr2O7 isomorphous miscibility range. Major attention has been focused on the pyrochlore-like (Nd2−xZrx)Zr2O7+x/2 solid solutions with x = 0–0.78, which are thought to be potential interstitial oxide ion conductors. The X-ray and neutron diffraction results demonstrate that the (Nd2−xZrx)Zr2O7+x/2 (x = 0–1.27) solid solutions undergo an order–disorder (pyrochlore–defect fluorite) structural phase transition. The (Nd2−xZrx)Zr2O7+x/2 (x = 0.2–0.78) have the bulk conductivity, ∼(1.2–4) 10–3 S/cm at 750 C, which is two orders of magnitude higher than that of the ordered pyrochlore Nd2Zr2O7. An attempt has been made to determine the interstitial oxygen content of (Nd2−xZrx)Zr2O7+x/2 (x = 0.2; 0.67) in a reducing atmosphere using thermogravimetry and mass spectrometry. It has been shown that no reduction occurs in the NdZrO system, where neodymium has only one oxidation state, 3+.
Keywords Fuel cells; Ionic conduction; Electrochemical impedance spectroscopy; Neutron diffraction; X-ray diffraction; SEM
Remark http://dx.doi.org/10.1016/j.jallcom.2014.03.068
Link
ID=252

Role of point defects in bipolar fatigue behavior of Bi(Mg1/2Ti1/2)O3 modified (Bi1/2K1/2)TiO3-(Bi1/2Na1/2)TiO3 relaxor ceramics

Authors Nitish Kumar, Troy Y. Ansell and David P. Cann
Source
J. Applied Physics
Volume: 115, Pages: 154104
Time of Publication: 2014
Abstract Lead-free Bi(Mg1/2Ti1/2)O3-(Bi1/2K1/2)TiO3-(Bi1/2 Na 1/2)TiO3 (BMT-BKT-BNT) ceramics have been shown to exhibit large electromechanical strains under high electric fields along with negligible fatigue under strong electric fields. To investigate the role of point defects on the fatigue characteristics, the composition 5BMT-40BKT-55BNT was doped to incorporate acceptor and donor defects on the A and B sites by adjusting the Bi/Na and Ti/Mg stoichiometries. All samples had pseudo-cubic symmetries based on x-ray diffraction, typical of relaxors. Dielectric measurements showed that the high and low temperature phase transitions were largely unaffected by doping. Acceptor doping resulted in the observation of a typical ferroelectric-like polarization with a remnant polarization and strain hysteresis loops with significant negative strain. Donor-doped compositions exhibited characteristics that were indicative of an ergodic relaxor phase. Fatigue measurements were carried out on all of the compositions. While the A-site acceptor-doped composition showed a small degradation in maximum strain after 106 cycles, the other compositions were essentially fatigue free. Impedance measurements were used to identify the important conduction mechanisms in these compositions. As expected, the presence of defects did not strongly influence the fatigue behavior in donor-doped compositions owing to the nature of their reversible field-induced phase transformation. Even for the acceptor-doped compositions, which had stable domains in the absence of an electric field at room temperature, there was negligible degradation in the maximum strain due to fatigue. This suggests that either the defects introduced through stoichiometric variations do not play a prominent role in fatigue in these systems or it is compensated by factors like decrease in coercive field, an increase in ergodicity, symmetry change, or other factors.
Remark http://dx.doi.org/10.1063/1.487167
Link
ID=251

Structure and transport properties in un-doped and acceptor-doped gadolinium tungstates

Authors Wen Xing, Protima Rauwel, Charles H. Hervoches, Zuoan Li, Reidar Haugsrud
Source
Solid State Ionics
Volume: 261, Pages: 87-94
Time of Publication: 2014
Abstract Nominal Gd6WO12, Gd5.94Ca0.06WO12 − δ, Gd5.7Ca0.3WO12 − δ and Gd5.7WO12 − δ were synthesized by solid state reaction and wet chemistry methods. The structure and morphology of the materials were analyzed by XRD, SEM and TEM and the electrical conductivity was measured as a function of temperature in reducing and oxidizing atmospheres under wet and dry conditions. The total conductivity is essentially independent of composition above 700 C. Below 700 C, the conductivity of Ca-doped samples is higher than that of Gd6WO12 and Gd5.7WO12 − δ and increases with increasing doping concentration. The conductivity below 700 C is also higher under wet compared to dry conditions and, moreover, the H–D isotope effect on the conductivity is significant. Based on this, and on conductivity characterization as a function of pO2pO2 and pH2OpH2O, it was concluded that the materials are mixed ionic and electronic conductors where electrons and holes dominate at high temperatures and intermediate temperatures under sufficiently reducing and oxidizing conditions, respectively. Protons are the predominating ionic charge carriers below approximately 700 C. The hydrogen flux through Gd5.7Ca0.3WO12 − δ was measured as a function of temperature under wet and dry sweep gas conditions, as well as with varying pH2pH2 on the feed side, confirming the picture outlined by the conductivity measurements. A defect chemical model has been derived to which the conductivity data were fitted yielding thermodynamic and transport parameters describing the functional characteristics of the materials.
Keywords Proton; Structure; Gd6WO12; Ambipolar conductivity; Hydrogen flux
Remark Link
ID=250

Solid Oxide-Molten Carbonate Nano-composite Fuel Cells: Particle Size Effect

Authors Shalima Shawuti, Mehmet A. Gulgun
Source
Journal of Power Sources
Time of Publication: 2014
Abstract Varying the amount of specific interface area in the CeO2-Na2CO3 nano-composite fuel cell electrolyte helped reveal the role of interfaces in ionic conductivity. We mixed ceria particles with micrometer or nanometer size distributions to obtain a specific surface area (SSA) in the composite from 47 m2/g to 203 m2/g. Micro-structural investigations of the nano-composite showed that the Na2CO3 phase serves as the glue in the microstructure, while thermal analysis revealed a glass transition-like behavior at 350 C. High SSA enhanced the ionic conductivity significantly at temperatures below 400 C. Moreover, the activation energy for the Arrhenius conductivity (σT) of the composites was lower than that of the Na2CO3 phase. This difference in the activation energies is consistent with the calculated dissociation energy of the carbonate phase. The strong dependence of conductivity on the SSA, along with differences in the activation energies, suggests that the oxide surface acted as a dissociation agent for the carbonate phase. A model for the solid composite electrolyte is proposed: in the nano-composite electrolyte, the oxide surface helps Na2CO3 dissociate, so that the "liberated" ions can move more easily in the interaction region around the oxide particles, thus giving rise to high ionic conductivities.
Keywords composite electrolyte; ionic conductivity; impedance spectroscopy; SOFC; interphase; activation energy
Remark in press, http://dx.doi.org/10.1016/j.jpowsour.2014.05.010
Link
ID=247

Doped Germanate-Based Apatites as Electrolyte for Use in Solid Oxide Fuel Cells

Authors S.-F. Wang, Y.-F. Hsu, W.-J. Lin and K. Kobayashi
Source
Fuel Cells
Time of Publication: 2014
Abstract Apatite ceramics, known for their good electrical conductivities, have garnered substantial attention as an alternative electrolyte for solid oxide fuel cells (SOFCs). However, studies focusing on the electrochemical performances of SOFCs with apatities as electrolytes remain rare, partly due to their high sintering temperature. In this study, the effects of Mg2+, Al3+, Ga3+, and Sn4+ dopants on the characteristics of La9.5Ge6O26  δ are examined and their potential for use as SOFC electrolytes evaluated. The results indicate that La9.5Ge5.5Al0.5O26 is stabilized into a hexagonal structure, while the La9.5Ge5.5Sn0.5O26.25, La9.5Ge5.5Ga0.5O26, and La9.5Ge5.5Mg0.5O25.75 ceramics reveal triclinic cells accompanied with the second phase La2Sn2O7 or La2GeO5. The study further demonstrates that a high sintering temperature is needed for both the La9.5Ge5.5Mg0.5O25.75 and the La9.5Ge5.5Sn0.5O26.25 ceramics, and the worst electrical conductivity among the examined systems appears in the La9.5Ge5.5Ga0.5O26 ceramic. The La9.5Ge5.5Al0.5O26 ceramic is accordingly selected for cell evaluation due to its ability to reach densification at 1,350 C, its good electrical conductivity of 0.026 S cm–1 at 800 C, and its acceptable thermal expansion coefficient of 10.1  10–6 K–1. The maximum power densities of the NiO-SDC/La9.5Ge5.5Al0.5O26/LSCF-SDC single cell are found to be respectively 0.22, 0.16, 0.11, and 0.07 W cm–2 at 950, 900, 850, and 800 C.
Keywords Apatites; Cell Performance; Electrolyte; Impedance; Solid Oxide Fuel Cell
Remark Article first published online: 19 FEB 2014 DOI: 10.1002/fuce.201300093
Link
ID=246

Effect of Nb substitution for Ti on the electrical properties of Yb2Ti2O7-based oxygen ion conductors

Authors L.G. Shcherbakova, J.C.C. Abrantes, D.A. Belov, E.A. Nesterova, O.K. Karyagina, A.V. Shlyakhtina
Source
Solid State Ionics
Time of Publication: 2014
Abstract We have studied the effect of niobium doping on the electrical conductivity of Yb2Ti2O7-based oxygen ion conductors. Yb2[Ti1 − xNbx]2O7 (x = 0.01, 0.04, 0.1) and (Yb0.8Tb0.1Ca0.1)2[Ti1 − xNbx]2O6.9 (x = 0; 0.05; 0.1) pyrochlore solid solutions were synthesized through coprecipitation followed by firing at 1550 C for 4 h. The materials were examined by XPS, XRD, scanning electron microscopy and impedance spectroscopy. Yb2(Ti0.99Nb0.01)2O7 was shown to have the highest oxygen ion conductivity in air (2.3 10− 3 S/cm at 750 C), which is however markedly lower than that of undoped Yb2Ti2O7. In the (Yb0.8Tb0.1Ca0.1)2[Ti1 − xNbx]2O6.9 (x = 0; 0.05; 0.1) system, the highest conductivity is offered by (Yb0.8Tb0.1Ca0.1)2[Ti0.95Nb0.05]2O6.9 (σ = 4.44 10− 3 S/cm at 650 C). Additional oxygen vacancies created by Ca doping in pyrochlore structure reduce the detrimental effect of Nb4 + doping on the oxide ion transport up to 5% Nb. The conductivity of the Yb2(Ti0.99Nb0.01)2O7 and (Yb0.8Tb0.1Ca0.1)2[Ti0.95Nb0.05]2O6.9 solid solutions was measured both in air and under reducing conditions (5% H2 in N2 and CO2 atmospheres). A comparative study of both these compositions under 5% H2 in N2 atmosphere showed that the transport mechanism was not affected by complex doping of the lanthanide and titanium sublattices in the Yb2Ti2O7-based materials and was related to oxygen vacancies. Conductivity measurements in CO2 were done to ensure correct evaluation of the ionic conductivity of (Yb0.8Tb0.1Ca0.1)2[Ti0.95Nb0.05]2O6.9, because in air it seems to be a mixed p-type and ionic conductor.
Keywords Oxide ion conductivity; Pyrochlore; Acceptor doping; Donor doping; Impedance spectroscopy
Remark Available online 1 February 2014; http://dx.doi.org/10.1016/j.ssi.2014.01.019
Link
ID=241

Characterisation of structure and conductivity of BaTi0.5Sc0.5O3 − δ

Authors S.M.H. Rahman, I. Ahmed, R. Haugsrud, S.G. Eriksson, C.S. Knee
Source
Solid State Ionics
Volume: 225, Pages: 140–146
Time of Publication: 2014
Abstract BaTi0.5Sc0.5O3 − δ was prepared via solid state reaction route and final sintering at 1550 C. High resolution X-ray powder diffraction on the as-prepared material reveals a cubic perovskite structure with a unit cell parameter, a = 4.1343(1) . Thermogravimetric analysis revealed the presence of significant levels of protons in the as-prepared material and 74% of the theoretically achievable protonation through filling of oxide ion vacancies was attained on exposure to a humid environment at 185 C. Infrared spectroscopy revealed a broad Osingle bondH stretching band confirming the presence of OHO• defects. Electrical conductivity was measured with variable frequency AC impedance methods in oxygen, argon, and hydrogen under dry, hydrated (H2O) and heavy water (D2O) conditions. In the temperature range of 150–550 C in a wet gas atmosphere the conductivity is significantly higher than that observed for dry conditions, indicating that protons are the dominant charge carriers. Conductivity is also found to be higher in dry oxygen in comparison with dry argon over the whole temperature range of 150–1000 C, characteristic of contribution from p-type charge carriers under oxidising atmospheres. At 550 C the proton conductivity was estimated to be 2.89 10− 4 S cm− 1 in wet Ar. Fitting of conductivity data provides a hydration enthalpy change (ΔHhydr0) of − 100 5 kJ/mol and hydration entropy change (ΔShydr0) of − 160 10 J/mol K.
Keywords Barium titanate; BaTiO3; Perovskite; Proton conductivity; X-ray diffraction; Hydration
Remark Link
ID=238

Polymorphism and properties of Bi2WO6 doped with pentavalent antimony

Authors E.P. Kharitonova, D.A. Belov, A.B. Gagor, A.P. Pietraszko, O.A. Alekseeva, V.I. Voronkova
Source
Journal of Alloys and Compounds
Time of Publication: 2014
Abstract Antimony-containing solid solutions isostructural with bismuth tungstate, Bi2WO6, have been prepared in air as polycrystalline samples by solid-state reactions and as single crystals by unseeded flux growth. The antimony in the solid solutions is in a pentavalent state and substitutes for tungsten in the structure of Bi2WO6. The Bi2W1–xSbxO6–y solid solutions have been shown to exist in the composition range 0 ⩽ x ⩽ 0.05. We have examined the effect of Sb5+ doping on the polymorphism and properties of Bi2WO6. In contrast to undoped Bi2WO6, antimony-substituted bismuth tungstate does not completely transform into its high-temperature, monoclinic phase at 960 C and remains two-phase up to temperatures approaching its melting point. Antimony substitution for tungsten has a weak effect on the temperatures of the ferroelectric phase transitions. Heterovalent substitution of Sb5+ for W6+ is accompanied by the formation of extra oxygen vacancies and an increase in the electrical conductivity of the solid solutions by one to two orders of magnitude relative to undoped Bi2WO6.
Keywords Aurivillius phases; Bi2WO6; Ceramics; Phase transitions; Electrophysical properties; Differential scanning calorimetry
Remark Available online 3 January 2014
Link
ID=237

Effect of Ni Concentration on Phase Stability, Microstructure and Electrical Properties of BaCe0.8Y0.2O3-δ - Ni Cermet SOFC Anode and its application in proton conducting ITSOFC

Authors Pooja Sawant, S. Varma, M.R. Gonal, B.N. Wani, Deep Prakash, S.R. Bharadwaj
Source
Electrochimica Acta
Time of Publication: 2013
Abstract In this work we have studied the effect of Ni concentration on phase stability, microstructure and electrical properties of BaCe0.8Y0.2O3-δ (BCY)-Ni cermet SOFC anode. It has been seen that Ni forms composite with BCY without forming any solid solution in both oxidized and reduced state. Also, microstructural analysis reveals the effect of Ni on porosity and triple phase boundaries necessary for electrochemical reactions during cell operation. Electrical conductivity values obtained from dc four probe technique in H2 atmosphere increase with an increase in Ni content. Composites with low vol% of Ni contents i.e. 19% (Ni19) and 26% (Ni26) show predominantly semiconductor-like behaviour whereas higher vol% viz. 35% (Ni35), 45% (Ni45) and 56% (Ni56) composites show electronic conductivity behaviour. This confirms that electronic conduction occurs through metallic Ni phase. Also, anode supported single cell for proton conducting SOFC has been fabricated using Ni35 composition and its current-potential characteristics measured at different temperatures.
Keywords Cermet; X-ray diffraction; Electrical conductivity; Four probe; Single Cell
Remark Available online 25 December 2013
Link
ID=228

Nanocrystalline Sm0.5Sr0.5CoO3−δ synthesized using a chelating route for use in IT-SOFC cathodes: microstructure, surface chemistry and electrical conductivity

Authors Rares Scurtu, Simona Somacescu, Jose Maria Calderon-Moreno, Daniela Culita, Ion Bulimestru, Nelea Popa, Aurelian Gulea, Petre Osiceanu
Source
Journal of Solid State Chemistry
Time of Publication: 2013
Abstract Nanocrystalline Sm0.5Sr0.5CoO3−δ powders were synthesized by a chelating route using different polyfunctional HxAPC acids (APC=aminopolycarboxylate; x= 3, 4, 5). Different homologous aminopolycarboxylic acids, namely nitrilotriacetic (H3nta), ethylenediaminetetraacetic (H4edta), 1,2-cyclohexanediaminetetracetic (H4cdta) and diethylenetriaminepentaacetic (H5dtpa) acid, were used as chelating agents to combine Sm, Sr, Co elements into a perovskite structure. The effects of the chelating agents on the crystalline structure, porosity, surface chemistry and electrical properties were investigated. The electrical properties of the perovskite-type materials emphasized that their conductivities in the temperature range of interest (600–800 C) depend on the nature of the precursors as well as on the presence of a residual Co oxide phase as shown by XRD and XPS analysis. The surface chemistry and the surface stoichiometries were determined by XPS revealing a complex chemical behavior of Sr that exhibits a peculiar „surface phase” and „bulk phase” chemistry within the detected volume (<10 nm).
Keywords Cathode; Perovkites; Electrical Conductivity; XPS; IT-SOFC
Remark Available online 5 November 2013
Link
ID=217

Synthesis, properties and phase transitions of pyrochlore- and fluorite-like Ln2RMO7 (Ln=Sm, Ho; R=Lu, Sc; M= Nb, Ta)

Authors A.V. Shlyakhtina, D.A. Belov, K.S. Pigalskiy, A.N. Shchegolikhin, I.V. Kolbanev, O.K. Karyagina
Source
Materials Research Bulletin
Time of Publication: 2013
Abstract We have studied the new compounds with fluorite-like (Ho2RNbO7 (R = Lu, Sc)) and pyrochlore-like (Sm2ScTaO7) structure as potential oxide ion conductors. The phase formation process (from 1200 to 1600 C) and physical properties (electrical, thermo mechanical, and magnetic) for these compounds were investigated. Among the niobate materials the highest bulk conductivity is offered by the fluorite-like Ho2ScNbO7 synthesized at 1600 C: 3.8 10−5 S/cm at 750 C, whereas in Sm system the highest bulk conductivity, 7.3 10−6 S/cm at 750 C, is offered by the pyrochlore Sm2ScTaO7 synthesized at 1400 C. In Sm2ScTaO7 pyrochlore we have observed the first-order phase transformation at ∼650–700 C is related to rearrangement process in the oxygen sublattice of the pyrochlore structure containing B-site cations in different valence state and actually is absent in the defect fluorites. The two holmium niobates show Curie–Weiss paramagnetic behavior, with the prevalence of antiferromagnetic coupling. The magnetic susceptibility of Sm2ScTaO7 is a weak function of temperature, corresponding to Van Vleck paramagnetism.
Keywords Pyrochlore; Fluorite; Phase transition; Ionic conductivity; Thermo mechanical analysis; Dielectric permittivity; Loss tangent; Magnetic susceptibility
Remark Available online 11 October 2013
Link
ID=215

The Investigation of E-beam Deposited Titanium Dioxide and Calcium Titanate Thin Films

Authors Kristina BOČKUTĖ, Giedrius LAUKAITIS, Darius VIRBUKAS, Darius MILČIUS
Source
MATERIALS SCIENCE (MEDIAGOTYRA)
Volume: 19, Issue: 3, Pages: 245-249
Time of Publication: 2013
Abstract Thin titanium dioxide and calcium titanate films were deposited using electron beam evaporation technique. The substrate temperature during the deposition was changed from room temperature to 600 C to test its influence on TiO2 film formation and optical properties. The properties of CaTiO3 were investigated also. For the evaluation of the structural properties the formed thin ceramic films were studied by X-ray diffraction (XRD), energy dispersive spectrometry (EDS), scanning electron microscopy (SEM) and atomic force microscopy (AFM). Optical properties of thin TiO2 ceramics were investigated using optical spectroscope and the experimental data were collected in the ultraviolet-visible and near-infrared ranges with a step width of 1 nm. Electrical properties were investigated by impedance spectroscopy.It was found that substrate temperature has influence on the formed thin films density. The density increased when the substrate temperature increased. Substrate temperature had influence on the crystallographic, structural and optical properties also.
Keywords electron beam evaporation; titanium oxide; calcium titanate; optical properties
Remark DOI: http://dx.doi.org/10.5755/j01.ms.19.3.1805
Link
ID=214

Synthesis and Characterization of Nonsubstituted and Substituted Proton-Conducting La6–xWO12–y

Authors Janka Seeger, Mariya E. Ivanova, Wilhelm A. Meulenberg, Doris Sebold, Detlev Stver, Tobias Scherb, Gerhard Schumacher, Sonia Escolstico, Cecilia Sols, and Jos M. Serra
Source
Inorganic Chemistry
Publisher: ACS Publications, Time of Publication: 2013
Abstract Mixed proton–electron conductors (MPEC) can be used as gas separation membranes to extract hydrogen from a gas stream, for example, in a power plant. From the different MPEC, the ceramic material lanthanum tungstate presents an important mixed protonic–electronic conductivity. Lanthanum tungstate La6–xWO12–y (with y = 1.5x + δ and x = 0.5–0.8) compounds were prepared with La/W ratios between 4.8 and 6.0 and sintered at temperatures between 1300 and 1500 C in order to study the dependence of the single-phase formation region on the La/W ratio and temperature. Furthermore, compounds substituted in the La or W position were prepared. Ce, Nd, Tb, and Y were used for partial substitution at the La site, while Ir, Re, and Mo were applied for W substitution. All substituents were applied in different concentrations. The electrical conductivity of nonsubstituted La6–xWO12–y and for all substituted La6–xWO12–y compounds was measured in the temperature range of 400–900 C in wet (2.5% H2O) and dry mixtures of 4% H2 in Ar. The greatest improvement in the electrical characteristics was found in the case of 20 mol % substitution with both Re and Mo. After treatment in 100% H2 at 800 C, the compounds remained unchanged as confirmed with XRD, Raman, and SEM.
Keywords ProGasMix
Remark lanthanum tungstate
La6–xWO12–y
Link
ID=213

Synthesis and Characterization of Nonsubstituted and Substituted Proton-Conducting La6–xWO12–y

Authors Janka Seeger, Mariya E. Ivanova, Wilhelm A. Meulenberg, Doris Sebold, Detlev Stver, Tobias Scherb, Gerhard Schumacher, Sonia Escolstico, Cecilia Sols, and Jos M. Serra
Source
Inorg. Chem.
Time of Publication: 2013
Abstract Mixed proton–electron conductors (MPEC) can be used as gas separation membranes to extract hydrogen from a gas stream, for example, in a power plant. From the different MPEC, the ceramic material lanthanum tungstate presents an important mixed protonic–electronic conductivity. Lanthanum tungstate La6–xWO12–y (with y = 1.5x + δ and x = 0.5–0.8) compounds were prepared with La/W ratios between 4.8 and 6.0 and sintered at temperatures between 1300 and 1500 C in order to study the dependence of the single-phase formation region on the La/W ratio and temperature. Furthermore, compounds substituted in the La or W position were prepared. Ce, Nd, Tb, and Y were used for partial substitution at the La site, while Ir, Re, and Mo were applied for W substitution. All substituents were applied in different concentrations. The electrical conductivity of nonsubstituted La6–xWO12–y and for all substituted La6–xWO12–y compounds was measured in the temperature range of 400–900 C in wet (2.5% H2O) and dry mixtures of 4% H2 in Ar. The greatest improvement in the electrical characteristics was found in the case of 20 mol % substitution with both Re and Mo. After treatment in 100% H2 at 800 C, the compounds remained unchanged as confirmed with XRD, Raman, and SEM.
Remark DOI: 10.1021/ic401104m; Publication Date (Web): September 3, 2013
Link
ID=208

Effects of Nb5+, Mo6+, and W6+ dopants on the germanate-based apatites as electrolyte for use in solid oxide fuel cells

Authors Sea-Fue Wang, Yung-Fu Hsu, Wan-Ju Lin
Source
International Journal of Hydrogen Energy
Volume: 38, Issue: 27, Pages: 12015–12023
Time of Publication: 2013-09
Abstract Rare information is available in the literature on the cell performance of the solid oxide fuel cells (SOFCs) using apatites known for their good electrical conductivity as electrolyte materials. In this study, La9.5Ge5.5Nb0.5O26.5, La9.5Ge5.5Mo0.5O26.75, and La9.5Ge5.5W0.5O26.75 ceramics were prepared and characterized. The results indicated that the La9.5Ge5.5Nb0.5O26.5 and La9.5Ge5.5W0.5O26.75 ceramics reported hexagonal phase, while the La9.5Ge5.5Mo0.5O26.75 ceramic demonstrated triclinic symmetry. Among the apatities evaluated, La9.5Ge5.5Nb0.5O26.5 sintered at 1450 C showed the best conduction with an electrical conductivity value of 0.045 S/cm at 800 C. Button cells of NiO–SDC/La9.5Ge5.5Nb0.5O26.5/LSCF–SDC were built and revealed good structural integrity. The total ohmic resistance (R0) and interfacial polarization resistance (RP) of the cell read 0.428 and 0.174 Ω cm2 and 0.871 and 1.164 Ω cm2, respectively at 950 and 800 C. The maximum power densities (MPD) of the single cell at 950 and 800 C were respectively 0.363 and 0.095 W cm−2. Without optimizing the anode and cathode as well as hermetic sealing of the cell against the gas, the study found the performance of the single cell with the pure La9.5Ge5.5Nb0.5O26.5 as its electrolyte material superior to those of the SOFC cells with a YSZ electrolyte of comparable thickness shown in the literature.
Keywords Solid oxide fuel cell; Apatite; Impedance; Cell performance
Remark Link
ID=207

Transformation from insulating p-type to semiconducting n-type conduction in CaCu3Ti4O12-related Na(Cu5/2Ti1/2)Ti4O12 ceramics

Authors Li, Ming, Sinclair, Derek C.
Source
Journal of Applied Physics
Volume: 114, Issue: 3, Pages: 034106 - 034106-8
Time of Publication: 2013-07
Abstract A double doping mechanism of Na+ + ½ Ti4+ → Ca2+ + ½ Cu2+ on the general formula Ca1-xNax(Cu3-x/2Tix/2)Ti4O12 has been used to prepare a series of isostructural CaCu3Ti4O12 (CCTO)-type perovskites. A complete solid solution exists for 0 ≤ x ≤ 1 and all compositions exhibit incipient ferroelectric behaviour with higher than expected intrinsic relative permittivity. Although CCTO ceramics typically exhibit n-type semiconductivity (room temperature, RT, resistivity of ∼10–100 Ω cm), Na(Cu5/2Ti1/2)Ti4O12 (NCTO) ceramics sintered at 950 C consist of two insulating bulk phases (RT resistivity > 1 GΩ cm), one p-type and the other n-type. With increasing sintering temperature/period, the p-type phase transforms into the n-type phase. During the transformation, the resistivity and activation energy for electrical conduction (Ea ∼ 1.0 eV) of the p-type phase remain unchanged, whereas the n-type phase becomes increasingly conductive with Ea decreasing from ∼ 0.71 to 0.11 eV with increasing sintering temperature. These changes are attributed to small variations in stoichiometry that occur during high temperature ceramic processing with oxygen-loss playing a crucial role.
Remark Link
ID=206

New double molybdate Na9Fe(MoO4)6: Synthesis, structure, properties

Authors Aleksandra A. Savina, Sergey F. Solodovnikov, Olga M. Basovich, Zoya A. Solodovnikova, Dmitry A. Belov, Konstantin V. Pokholok, Irina A. Gudkova, Sergey Yu. Stefanovich, Bogdan I. Lazoryak, Elena G. Khaikina
Source
Journal of Solid State Chemistry
Volume: 205, Pages: 149–153
Time of Publication: 2013-09
Abstract A new double molybdate Na9Fe(MoO4)6 was synthesized using solid state reactions and studied with X-ray powder diffraction, second harmonic generation (SHG) technique, differential scanning calorimetry, X-ray fluorescence analysis, Mssbauer and dielectric impedance spectroscopy. Single crystals of Na9Fe(MoO4)6 were obtained and its structure was solved (the space group RView the MathML source3, a=14.8264(2), c=19.2402(3) , V=3662.79(9) 3, Z=6, R=0.0132). The structure is related to that of sodium ion conductor II-Na3Fe2(AsO4)3. The basic structure units are polyhedral clusters composed of central FeО6 octahedron sharing edges with three Na(1)О6 octahedra. The clusters share common vertices with bridging МоО4 tetrahedra to form an open 3D framework where the cavities are occupied by Na(2) and Na(3) atoms. The compound melts incongruently at 904.70.2 K. Arrhenius type temperature dependence of electric conductivity σ has been registered in solid state (σ=6.810−2 S сm−1 at 800 K), thus allowing considering Na9Fe(MoO4)6 as a new sodium ion conductor.
Keywords Sodium–iron molybdate; Crystal structure; Solid-state electrolyte
Remark Link
ID=205

Study of bulk and grain-boundary conductivity of Ln2+xHf2−xO7−δ (Ln = Sm-Gd; x = 0, 0.096) pyrochlores

Authors A. V. Shlyakhtina, S. N. Savvin, A. V. Levchenko, A. V. Knotko, Petra Fedtke, Andreas Busch, Torsten Barfels, Marion Wienecke, L. G. Shcherbakova
Source
Journal of Electroceramics
Volume: 24, Issue: 4, Pages: 300-307
Time of Publication: 2010-06
Abstract The electrical conductivity of new solid electrolytes Eu2.096Hf1.904O6.952 and Gd2Hf2O7 have been compared with those for different pyrochlores including titanates and zirconates Ln2+xМ2−xO7−δ (Ln = Sm-Lu; M = Ti, Zr; x = 0−0.81). Impedance spectroscopy data demonstrate that Eu2.096Hf1.904O6.952 and Gd2Hf2O7 synthesized from mechanically activated oxides have high ionic conductivity, comparable to that of their zirconate analogues. The bulk and grain-boundary components of conductivity in Sm2.096Hf1.904O6.952 (Тsynth = 1600С), Eu2.096Hf1.904O6.952 and Gd2Hf2O7 (Тsynth = 1670С) have been determined. The highest bulk conductivity is offered by the disordered pyrochlores prepared at 1600C and 1670C: ~1.5  10−4 S/cm for Sm2.096Hf1.904O6.952, 5  10−3 S/cm for Eu2.096Hf1.904O6.952 and 3  10−3 S/cm for Gd2Hf2O7 at 780С, respectively. The conductivity of the fluorite-like phases at the phase boundaries of the Ln2+xМ2−xO7−δ (Ln = Eu, Gd; M = Zr, Hf; x ~ 0.286) solid solutions, as well as that of the high-temperature fluorite-like phases Ln2+xМ2−xO7−δ (Ln = Eu, Gd; M = Zr, Hf; x = 0−0.286), is lower than the conductivity of the disordered pyrochlores Ln2+xМ2−xO7−δ (Ln = Eu, Gd; M = Zr, Hf; x = 0−0.096).
Remark Link
ID=203

Solid-state photoelectrochemical H2 generation with gaseous reactants

Authors Kingsley O. Iwu, Augustinas Galeckas, Andrej Yu. Kuznetsov, Truls Norby
Source
Electrochimica Acta
Volume: 97, Pages: 320–325
Time of Publication: 2013-05
Abstract Photocurrent and H2 production were demonstrated in an all solid-state photoelectrochemical cell employing gaseous methanol and water vapour at the photoanode. Open circuit photovoltage of around -0.4 V and short circuit photocurrent of up to 250 μA/cm2 were obtained. At positive bias, photocurrent generation was limited by the irradiance, i.e., the amount of photogenerated charge carriers at the anode. Time constants and impedance spectra showed an electrochemical capacitance of the cell of about 15 μF/cm2 in the dark, which increased with increasing irradiance. With only water vapour at the anode, the short circuit photocurrent was about 6% of the value with gaseous methanol and water vapour. The photoanode and electrocatalyst on carbon paper support were affixed to the proton conducting membrane using Nafion as adhesive, an approach that yielded photocurrents up to 15 times better than that of a cell assembled by hot-pressing, in spite of the overall cell resistance of the latter being up to 5 times less than that of the former. This is attributed, at least partially, to reactants being more readily available at the photoanode of the better performing cell.
Keywords Photoelectrochemical; hydrogen; TiO2; solid-state; Nafion
Remark Link
ID=201

Synthesis and characterization of perovskite-type SrxY1−xFeO3−δ (0.63≤x<1.0) and Sr0.75Y0.25Fe1−yMyO3−δ (M= Cr, Mn, Ni), (y=0.2, 0.33, 0.5)

Authors J.J. Biendicho, S. Shafeie, L. Frenck, D. Gavrilova, S. Bhme, A.M. Bettanini, P. Svedlindh, S. Hull, Z. Zhao, S.Ya. Istomin, J. Grins, G. Svensson
Source
Journal of Solid State Chemistry
Volume: 200, Pages: 30-38
Time of Publication: 2013-04
Abstract Abstract Oxygen-deficient ferrates with the cubic perovskite structure SrxY1−xFeO3−δ were prepared in air (0.71≤x≤0.91) as well as in N2 (x=0.75 and 0.79) at 1573 K. The oxygen content of the compounds prepared in air increases with increasing strontium content from 3-δ=2.79(2) for x=0.75 to 3-δ=2.83(2) for x=0.91. Refinement of the crystal structure of Sr0.75Y0.25FeO2.79 using TOF neutron powder diffraction (NPD) data shows high anisotropic atomic displacement parameter (ADP) for the oxygen atom resulting from a substantial cation and anion disorder. Electron diffraction (ED) and high-resolution electron microscopy (HREM) studies of Sr0.75Y0.25FeO2.79 reveal a modulation along <1 0 0>p with G ~0.4<1 0 0>p indicating a local ordering of oxygen vacancies. Magnetic susceptibility measurements at 5–390 K show spin-glass behaviour with dominating antiferromagnetic coupling between the magnetic moments of Fe cations. Among the studied compositions, Sr0.75Y0.25FeO2.79 shows the lowest thermal expansion coefficient (TEC) of 10.5 ppm K−1 in air at 298–673 K. At 773–1173 K TEC increases up to 17.2 ppm K−1 due to substantial reduction of oxygen content. The latter also results in a dramatic decrease of the electrical conductivity in air above 673 K. Partial substitution of Fe by Cr, Mn and Ni according to the formula Sr0.75Y0.25Fe1−yMyO3−δ (y=0.2, 0.33, 0.5) leads to cubic perovskites for all substituents with y=0.2. Their TECs are higher in comparison with un-doped Sr0.75Y0.25FeO2.79. Only M=Ni has increased electrical conductivity compared to un-doped Sr0.75Y0.25FeO2.79.
Keywords Perovskites; Neutron diffraction; Electron diffraction; High-temperature conductivity; Thermal expansion; Magnetic susceptibility
Remark Link
ID=200

Optimization of synthesis conditions for rare-earth titanate based oxygen ion conductors

Authors A.V. Shlyakhtina, D.A. Belov, S.Yu. Steafanovich, E.A. Nesterova, O.K. Karyagina, L.G. Shcherbakova
Source
Solid State Ionics
Volume: 230, Pages: 52-58
Time of Publication: 2013-01
Abstract High-density (Yb0.9Ca0.1)2Ti2O6.9, (Yb0.8Ca0.1Tb0.1)2Ti2O7 − δ, and (Dy0.8Ca0.1Tb0.1)2Ti2O7 − δ solid solutions have been prepared through co-precipitation followed by firing for 4 h at 1500 and 1550 C, and their crystal structure (XRD), microstructure (SEM), and oxygen ion conductivity (impedance spectroscopy) have been studied in relation to the firing temperature and precipitant used. As in the case of (Yb0.9Ca0.1)2Ti2O6.9 and (Yb0.8Ca0.1Tb0.1)2Ti2O7 − δ, the optimal synthesis temperature for (Dy0.8Ca0.1Tb0.1)2Ti2O7 − δ is 1500 C. The bulk oxygen ion conductivity of the pyrochlore-like solid solutions (Yb0.9Ca0.1)2Ti2O6.9 is a stronger function of synthesis temperature than that of the (Dy0.8Ca0.1Tb0.1)2Ti2O7 − δ and (Yb0.8Ca0.1Tb0.1)2Ti2O7 − δ solid solutions with more complex A sublattice. The rise of the synthesis temperature from 1500 to 1550 C has detrimental effect on the grain boundary conductivity of the (Yb0.9Ca0.1)2Ti2O6.9 and (Dy0.8Ca0.1Tb0.1)2Ti2O7 − δ ceramics. That effect is connected with a considerable grain-boundary segregation of a calcium-containing phase in the (Yb0.9Ca0.1)2Ti2O6.9 and (Dy0.8Ca0.1Tb0.1)2Ti2O7 − δ. The bulk and grain boundary conductivity of (Dy0.8Ca0.1Tb0.1)2Ti2O7 − δ are independent of the precursor synthesis conditions (homogeneous and non-homogeneous co-precipitation).
Keywords Synthesis; Co-precipitation; Pyrochlore; Doping; Oxide ion conductivity; Impedance spectroscopy
Remark Link
ID=195

H and Li Related Defects in ZnO and their Effect on Electrical Properties

Authors Tor Svendsen Bjrheim , Skjalg Erdal , Klaus Magnus Johansen , Knut Erik Knutsen , and Truls Norby
Source
J. Phys. Chem. C
Volume: 166, Issue: 44, Pages: 23764–23772
Time of Publication: 2012-10
Abstract Li and H are important electrically active impurities in ZnO and this work presents a detailed experimental and computational study of the behavior of H and Li in ZnO, and their effect on its defect structure. We employ AC conductivity measurements as a function of temperature and partial pressure of O2, H2O and D2O, which is combined with first principles density functional theory (DFT) calculations and thermodynamic modeling (TDM) of finite temperature defect structures in undoped and Li doped ZnO. Undoped ZnO is dominated by protons as hydroxide defects (OH_O^•), oxygen vacancies (v_O^(••)) and electrons under a large variety of atmospheric conditions, and we also predict from DFT and TDM the substitutional hydride ion (H_O^•) to dominate concentration-wise under the most reducing conditions at temperatures above 500 C. The equilibrium concentrations of defects in ZnO are small, and dopants such as Li strongly affect the electrical properties. Experimentally, Li doped ZnO is found to be n-type under all available atmospheric conditions and temperatures, with a n-type conductivity significantly lower than that of as-grown ZnO. The n-type conductivity also increases with decreasing p_(O_2 ) and with increasing p_(H_2 O). The observed electrical properties of Li doped ZnO are attributed to dominance of the ionic defects Li_Zn^/, OH_O^•, Li_i^•, v_O^(••), and the neutral complexes (Li_Zn OH_O)^ and (Li_Zn Li_i)^. Although Li doping lowers the Fermi level of as-grown ZnO significantly, low formation energy of the ionic donors, and passivation of Li_Zn^/ in the form of (Li_Zn OH_O)^ and (Li_Zn Li_i)^, prevents realization of significant/stable p-type activity in Li doped ZnO under equilibrium conditions.
Remark Link
ID=191

Characteristics of SrCo1 − xSnxO3 − δ cathode materials for use in solid oxide fuel cells

Authors Sea-Fue Wang, Yung-Fu Hsu, Chun-Ting Yeh, Chien-Chung Huang, Hsi-Chuan Lu
Source
Solid State Ionics
Volume: 227, Pages: 10–16
Time of Publication: 2012-10
Abstract In this study, introduction of tin ions in the SrCoO3 − δ oxide is attempted to modify its electrochemical behavior for serving as a cathode of intermediate-temperature solid oxide fuel cells (IT-SOFCs). Doping of tin ions appears to stabilize the cubic Pm-3m phase of the SrCo1 − ySnyO3 − δ ceramics but generates SrSnO3 precipitates and inhibits the grain growth as y value rises to a level greater than 10%. Obtained at 550 C, the maximum electrical conductivity of SrCo0.95Sn0.05O3 − δ reads 545 S cm− 1. Single cells with a structure of NiO–Sm0.2Ce0.8O2 − δ (SDC)/SDC/SrCo0.95Sn0.05O3 − δ–SDC are built and characterized. Though SrCo0.95Sn0.05O3 − δ is regarded as an MIEC (mixed ionic/electronic conductivity material), adding SDC to SrCo0.95Sn0.05O3 − δ guarantees good adhesion to and fine electrical contact with the electrolyte layer, thereby contributing to the reduction in R0 and RP values. The single cell with the SrCo0.95Sn0.05O3 − δ–SDC composite cathode at 700 C registers respectively an R0 value of 0.044 Ω cm2 and an RP value of 0.109 Ω cm2. In the absence of microstructure optimization and hermetic sealing of cells, a high power density of 0.847 W cm− 2 is reached. SrCo1 − ySnyO3 − δ thus emerges to be a promising cathode material for IT-SOFCs applications.
Keywords Solid oxide fuel cell; Cathode; Impedance; Cell performance
Remark Link
ID=190

Investigation of La1−xSrxCrO3−∂ (x ~ 0.1) as Membrane for Hydrogen Production

Authors Yngve Larring, Camilla Vigen, Florian Ahouanto, Marie-Laure Fontaine, Thijs Peters, Jens B. Smith, Truls Norby and Rune Bredesen
Source
Membranes
Volume: 2, Issue: 3, Pages: 665-686
Time of Publication: 2012-09
Abstract Various inorganic membranes have demonstrated good capability to separate hydrogen from other gases at elevated temperatures. Hydrogen-permeable, dense, mixed proton-electron conducting ceramic oxides offer superior selectivity and thermal stability, but chemically robust candidates with higher ambipolar protonic and electronic conductivity are needed. In this work, we present for the first time the results of various investigations of La1−xSrxCrO3−∂ membranes for hydrogen production. We aim in particular to elucidate the material’s complex transport properties, involving co-ionic transport of oxide ions and protons, in addition to electron holes. This opens some new possibilities for efficient heat and mass transfer management in the production of hydrogen. Conductivity measurements as a function of pH2 at constant pO2 exhibit changes that reveal a significant hydration and presence of protons. The flux and production of hydrogen have been measured under different chemical gradients. In particular, the effect of water vapor in the feed and permeate gas stream sides was investigated with the aim of quantifying the ratio of hydrogen production by hydrogen flux from feed to permeate and oxygen flux the opposite way (“water splitting”). Deuterium labeling was used to unambiguously prove flux of hydrogen species.
Keywords hydrogen transport membrane; proton permeation; oxygen permeation; water splitting
Remark Link
ID=183

BaTiO3–Bi(Zn1/2Ti1/2)O3–BiScO3 Ceramics for High-Temperature Capacitor Applications

Authors Natthaphon Raengthon, Tutu Sebastian, Denis Cumming, Ian M. Reaney, David P. Cann
Source
Journal of the American Ceramic Society
Volume: 95, Issue: 11, Pages: 3554–3561
Time of Publication: 2012-09
Abstract Ceramics based on solid solutions of xBaTiO3–(100−x)(0.5Bi(Zn1/2Ti1/2)O3–0.5BiScO3), where x = 50, 55, and 60 were prepared by solid-state reaction which resulted in a single perovskite phase with pseudocubic symmetry. Dielectric property measurements revealed a high relative permittivity (>1000), which could be modified with the addition of Bi(Zn1/2Ti1/2)O3 (BZT) and BiScO3 (BS) to engineer a temperature-stable dielectric response with a temperature coefficient of permittivity (TCε) as low as −182 ppm/C. By incorporating 2 mol% Ba vacancies into the stoichiometry, the resistivity increased significantly, especially at high temperatures (>200C). Vogel–Fulcher analysis of the permittivity data showed that the materials exhibited freezing of polar nanoregions over the range of 100–150 K. An analysis of optical absorption near the band edge for the Ba-deficient compositions suggested that the enhanced resistivity values were linked to a decrease in the concentration of defect states. An activation energy of ~1.4 eV was obtained from DC resistivity measurements suggesting that an intrinsic conduction mechanism played a major role in the high temperature conductivity. Finally, multilayer capacitors based on these compositions were fabricated, which exhibited dielectric properties comparable to the bulk material. Based on these results, this family of materials has great promise for high-temperature capacitor applications.
Remark Link
ID=182

Sr1−xPrxCo0.95Sn0.05O3−δ ceramic as a cathode material for intermediate-temperature solid oxide fuel cells

Authors Sea-Fue Wang, Yung-Fu Hsu, Hsi-Chuan Lu, Chien-Chung Huang, Chun-Ting Yeh
Source
International Journal of Hydrogen Energy
Volume: 37, Issue: 17, Pages: 12548–12556
Time of Publication: 2012-10
Abstract In this study, the physical properties of the Sr1−xPrxCo0.95Sn0.05O3−δ ceramics were measured and their potential for use as a cathode material of intermediate-temperature solid oxide fuel cells (IT-SOFCs) was evaluated. A cubic phase was retained in all of the Sr1−xPrxCo0.95Sn0.05O3−δ ceramics. Analysis of the temperature-dependent conductivity found the SrCo0.95Sn0.05O3−δ and Sr0.9Pr0.1Co0.95Sn0.05O3−δ ceramics exhibiting semiconductor-like behavior below 550 C and metal-like behavior above the same temperature. The Sr0.8Pr0.2Co0.95Sn0.05O3−δ and Sr0.7Pr0.3Co0.95Sn0.05O3−δ ceramics, however, reported a metal-like conductivity in the whole temperature range. The electrical conductivities of the Sr0.8Pr0.2Co0.95Sn0.05O3−δ ceramic at 500 C and 700 C read respectively 1250 S/cm and 680 S/cm, both of which were superior than those in most of the common perovskites. Single cells with a structure of NiO–Sm0.2Ce0.8O2−δ (SDC)/SDC/Sr0.8Pr0.2Co0.95Sn0.05O3−δ-SDC were built and characterized. Addition of SDC in Sr0.8Pr0.2Co0.95Sn0.05O3−δ emerged to be a crucial factor reducing the ohmic resistance (R0) and polarization resistance (RP) of the cell by facilitating a better adhesion to and electrical contact with the electrolyte layer. The R0 and RP of the cell read respectively 0.068 Ω cm2 and 0.0571 Ω cm2 at 700 C and 0.298 Ω cm2 and 1.310 Ω cm2 at 550 C. With no microstructure optimization and hermetic sealing of the cells, maximum power density (MPD) and open circuit voltage (OCV) reached respectively 0.872 W/cm2 and 0.77 V at 700 C and 0.482 W/cm2 and 0.86 V at 550 C. It is evident that Sr1−xPrxCo0.95Sn0.05O3−δ is a promising cathode material for IT-SOFCs.
Keywords Solid oxide fuel cell; Cathode; Impedance; Cell performance
Remark Link
ID=181

Nitrogen and hydrogen defect equilibria in Ca12Al14O33: a combined experimental and computational study

Authors Jonathan M. Polfus , Kazuaki Toyoura , Charles H. Hervoches , Martin F. Sunding , Isao Tanaka and Reidar Haugsrud
Source
Journal of Materials Chemistry
Volume: 22, Pages: 15828-15835
Time of Publication: 2012-07
Abstract The defect structure of mayenite is investigated by Density Functional Theory (DFT) defect calculations; in situ electrical conductivity measurements in NH3 atmosphere at high temperature; and X-ray photoelectron spectroscopy (XPS) and gas phase mass spectrometry (GP-MS) of NH3 treated specimens. The computational results suggest that nitrogen is primarily incorporated substitutionally on oxygen sites as NH−2 and N3−. The concentration of nitrogen was estimated to be within the same order of magnitude by XPS, GP-MS and DFT, yielding a stoichiometry close to Ca12Al14O31.5N0.5:(NH2)0.5O0.5 which corresponds well with that obtained by Boysen et al. from similarly treated samples. Out diffusion of nitrogen was found to occur around 700 C in Ar by XPS, GP-MS and conductivity measurements, also in accordance with Boysen et al. The conductivity measurements showed that NH3 treatment had a significant effect on the defect structure of the material which became evident only after replacing the NH3 atmosphere with Ar: the conductivity increased abruptly due to a temporary non-equilibrium reduction of the material as nitrogen diffuses out while the lack of a sufficiently large source of oxygen in the surrounding atmosphere prevents the specimen from re-oxidizing. Further, based on the computational results and the pH2 dependency on conductivity after NH3 treatment, we propose dissolution of hydride ions from H2 in the reduced and highly conductive post-NH3 state.
Remark Link
ID=178

Nd-doped Ba(Ce,Zr)O3 − δ proton conductors for application in conversion of CO2 into liquid fuels

Authors Wojciech Zając , Emil Hanc, Agnieszka Gorzkowska-Sobas, Konrad Świerczek, Janina Molenda
Source
Solid State Ionics
Volume: 225, Pages: 297–303
Time of Publication: 2012-10
Abstract The paper presents crystal structure, transport properties, chemical stability in CO2 atmosphere and thin film membrane preparation for materials from the Ba(Ce1 − xZrx)0.9Nd0.1O2.95 (x = 0, 0.25, 0.5, 0.75, 1) group of perovskite-type structure oxides. Transformation of crystal structure from orthorhombic Pnma to orthorhombic Imma and cubic with increasing xZr was observed along with linear decrease of pseudo-cubic unit cell volume and free lattice volume. Electrical conductivity of bulk and grain boundary was determined in dry air, as well as in air humidified with H2O or D2O. The highest proton conductivity was observed for material with xZr = 0.25. Further increase of Zr content led to decrease of conductivity as high as 2 orders of magnitude. This effect was coupled with bell-shape dependence of activation energy and pre-exponential term. Such behavior was explained as superimposed effects of high proton mobility for zirconium-rich materials due to cubic symmetry and cerium-rich materials due to softness of oxygen–oxygen separation distance, along with high proton concentration for cerium-rich perovskites. The deteriorating effect of grain boundaries on total electrical conductivity was far more pronounced for Zr-rich materials than in the case of Ce-rich ones. Declining grain boundary conductivity was attributed to both increase of number of grain boundaries and decrease of inherent grain boundary conductivity for Zr-rich samples. The highest chemical stability in CO2 atmosphere was achieved for high-Zr content materials, on the contrary, for BaCe0.9Nd0.1O2.95 in CO2 atmosphere, the decomposition onset temperature was below 500 C. 2 μm thin film membrane of Ba(Ce0.75Zr0.25)0.9Nd0.1O2.95 was successfully prepared on c-plane sapphire and fused silica substrates. Film's crystal structure matched that of the bulk material. The electrical conductivity of thermally treated film obtained on c-plane sapphire in wet air was 3.7 10− 4 S cm− 1 at 600 C.
Keywords Proton conductors; BaCeO3–BaZrO3 solid solutions; Isotope effect; Grain boundary effect; Thin films
Remark Link
ID=176

Hydrogen permeation, transport properties and microstructure of Ca-doped LaNbO4 and LaNb3O9 composites

Authors Wen Xing, Guttorm E. Syvertsen, Tor Grande, Zuoan Li, Reidar Haugsrud
Source
Journal of Membrane Science
Volume: 415-416, Pages: 878–885
Time of Publication: 2012-10
Abstract Two composites consisting of the proton conducting Ca-doped LaNbO4 and electron conducting LaNb3O9 with respectively 90 and 70 vol% LaNbO4 were prepared by spark plasma sintering. The amount of hydrogen produced at the sweep side was measured as a function of temperature and pH2 gradient under wet and dry sweep gas conditions. The hydrogen flux increases with increasing temperature and feed-sidepH2. The flux is significantly higher for the 70 vol% LaNbO4 composite than the 90 vol% LaNbO4 composite. Ambipolar conductivities calculated from the flux data showed the same pH2 dependence for both composites. The electrical conductivity of the 70 vol% LaNbO4 composite was characterized as a function of temperature under wet hydrogen. The microstructure and phase distribution of the two composites are analyzed and their transport properties with different flux limiting processes are discussed. An increased hydrogen production with wet compared to dry sweep gas is concluded to reflect water splitting due to transport of oxygen from the permeate to the feed side.
Keywords Hydrogen flux; Proton conductivity; Ceramic-ceramic composite; LaNbO4; LaNb3O9; Ambipolar conductivity; Water splitting
Remark Link
ID=174

High Power Plasma Sprayed Intermediate Temperature Solid Oxide Fuel Cells with Sm0.5Sr0.5CoO3-δ Cathode

Authors Chang-sing Hwang , Chun-Huang Tsai, Chun-Liang Chang, Jen-Feng Yu, Sheng-Hui Nien
Source
Procedia Engineering
Volume: 36, Pages: 81–87
Time of Publication: 2012-05
Abstract The cells with porous Ni/Fe(∼10 wt%) metal plate as a supporting substrate, double layers of La0.75Sr0.25Cr0.5Mn0.5 O3-δ (LSCM) and nanostructured Ce0.55La0.45O2-δ/Ni (LDC/Ni) as an anode, LDC as an anode interlayer, La0.8Sr0.2Ga0.8Mg0.2O3-δ (LSGM) as an electrolyte, LSGM/Sm0.5Sr0.5CoO3-δ (SSC) as a cathode interlayer and SSC as a cathode current collector, were prepared by atmospheric plasma spraying (APS) coating processes followed by a heating treatment. The current-voltage-power and AC impedance measurement results show that the prepared cell heat-treated at 850 C for 3 hours in air with a dead load of 1000 g cm-2 has an attracting performance. The measured maximum output power densities of this cell have reached 0.777, 0.742, 0.659, 0.542, 0.393, and 0.250 W cm-2 at 800, 750, 700, 650, 600, and 550 C respectively. The measured ohmic and polarization resistances are 0.241, 0.254, 0.282, 0.328, 0.42, 0.62 and 0.055, 0.064, 0.083, 0.128, 0.23, 0.471 Ω cm2 at 800, 750, 700, 650, 600, and 550 C respectively. After correction of the resistance inside the ProboStat system, the predicted actual maximum power densities that a cell can deliver are 1.95, 1.613, 1.186, 0.823, 0.512, and 0.293 W cm-2 at 800, 750, 700, 650, 600, and 550 C respectively.
Keywords Atmospheric plasma spray; solid oxide fuel cells; metal-supported; nanostructured; Sm0.5Sr0.5CoO3-δ
Remark Link
ID=170

Polymorphism and Oxide Ion Migration Pathways in Fluorite-Type Bismuth Vanadate, Bi46V8O89

Authors Xiaojun Kuang, Julia L. Payne, James D. Farrell, Mark R. Johnson, and Ivana Radosavljevic Evans
Source
Chem. Mater.
Volume: 24, Issue: 11, Pages: 2162–2167
Time of Publication: 2012-05
Abstract We report the synthesis, structural characterization, and ionic conductivity measurements for a new polymorph of bismuth vanadate Bi46V8O89, and an ab initio molecular dynamics study of this oxide ion conductor. Structure determination was carried out using synchrotron powder X-ray and neutron diffraction data; it was found that β-Bi46V8O89 crystallizes in space group C2/m and that the key differences between this and the previously reported α-form are the distribution of Bi and V cations and the arrangement of the VO4 coordination polyhedra in structure. β-Bi46V8O89 exhibits good oxide ion conductivity, with σ = 0.01–0.1 S/cm between 600 and 850 C, which is about an order of magnitude higher than yttria stabilized zirconia. The ab initio molecular dynamics simulations suggest that the ion migration pathways include vacancy diffusion through the Bi–O sublattice, as well as the O2– exchanges between the Bi–O and the V–O sublattices, facilitated by the variability of the vanadium coordination environment and the rotational freedom of the VOx coordination polyhedra.
Keywords Oxide ion conductors; bismuth vanadates; X-ray and neutron diffraction; AIMD simulations
Remark Publication Date (Web): May 3, 2012
Link
ID=169

SrCo1−xSbxO3−δ cathode materials prepared by Pechini method for solid oxide fuel cell applications

Authors Sea-Fue Wang, Hsi-Chuan Lu, Yung-Fu Hsu, Chien-Chung Huang, Chun-Ting Yeh
Source
Ceramics International
Volume: 38, Issue: 7, Pages: 5941–5947
Time of Publication: 2012-09
Abstract In this study, SrCo1−ySbyO3−δ powders were prepared by a modified Pechini method. According to the study results, the cubic Pm3m phase of the SrCo1−ySbyO3−δ ceramics was obtained as 10% of cobalt ions were substituted by antimony ions. Doping of Sb3+ ions appeared both to stabilize the Pm3m phase of the SrCo1−ySbyO3−δ ceramics and to enhance densification and retard grain growth. The coefficient of thermal expansion of the SrCo1−xSbxO3−δ ceramics increased with the content of the antimony ions, ranging from 10.17 to 15.37 ppm/C at temperatures lower than the inflection point (ranging from 450 C to 550 C) and from 22.16 to 29.29 ppm/C at higher temperatures. For the SrCo0.98Sb0.02O3−δ ceramic, electrical conductivity reached a maximum of 507 S/cm at 450 C. The ohmic and polarization resistances of the single cell with the pure SrCo0.98Sb0.02O3−δ cathode at 700 C read respectively 0.298 Ω cm2 and 0.560 Ω cm2. The single cell with the SrCo0.98Sb0.02O3−δ-SDC composite cathode appeared to reduce the impedances with the R0 and RP at 700 C reading respectively 0.109 Ω cm2 and 0.127 Ω cm2. Without microstructure optimization and measured at 700 C, the single cells with the pure SrCo0.98Sb0.02O3−δ cathode and the SrCo0.98Sb0.02O3−δ-SDC composite cathode, demonstrated maximum power densities of 0.100 W/cm2 and 0.487 W/cm2. Apparently, SrCo1−ySbyO3−δ is a potential cathode for use in IT-SOFCs.
Keywords Solid oxide fuel cell; Cathode; Impedance; Cell performance
Remark Available online 19 April 2012
Link
ID=166

Preparation and characterization of composite membranes based on sulfonated PEEK and AlPO4 for PEMFCs

Authors Vijay Shankar Rangasamy, Savitha Thayumanasundaram, Niels De Greef, Jin Won Seo, Jean-Pierre Locquet
Source
Solid State Ionics
Volume: 219, Pages: 83–89
Time of Publication: 2012-05
Abstract Sulfonated poly(ether ether ketone) (PEEK) and their composites are considered one of the most promising alternatives for Nafion, the industry benchmark for electrolytic membranes in proton exchange membrane (PEM) fuel cells. In the present study, PEEK was non-homogeneously sulfonated using concentrated H2SO4 at different temperatures (room temperature, 60 C, and 80 C) and time durations (5, 7, 48, and 72 h). Composite membranes of SPEEK with different weight ratios of AlPO4 synthesized by sol–gel were also prepared. Depending on the degree of sulfonation (DS), the Ion Exchange Capacity (IEC) of the membranes varied from 1.06 to 2.9 meq g− 1. XRD results show the increasing amorphous nature of the membranes with increase in IEC and DS value. The water uptake of the membranes also increased with DS. Simultaneous TGA–FTIR measurement of the composite membranes showed better thermal stability compared to pure SPEEK membranes. The water uptake and proton conductivity of the composite SPEEK membranes were found to be lower than that of pure SPEEK membranes, while the composite membranes exhibited a better swelling behavior and mechanical stability than the pure SPEEK samples.
Keywords Proton exchange membrane (PEM); Composite membranes; Sulfonated poly(etheretherketone) (SPEEK); Proton conductivity; Ion exchange capacity (IEC); Sol–gel
Remark Link
ID=162

Stability of (Ln0.8Ca0.1Ln′0.1)2Ti2O7−δ (Ln=Dy, Yb; Ln′=Ce, Tb) and (Tb0.9Ca0.1)2Ti2O7−δ pyrochlores under redox conditions

Authors S.N. Savvin, A.V. Shlyakhtina, D.A. Belov, J.C. Ruiz-Morales, L.G. Shcherbakova, P. Nuez
Source
Solid State Ionics
Volume: 225, Pages: 457–463
Time of Publication: 2012-10
Abstract The stability of (Ln0.8Ca0.1Ln′0.1)2Ti2O7−δ (Ln=Dy, Yb; Ln′=Ce, Tb) pyrochlores under different redox conditions (air, dry and wet H2) has been studied. The bulk conductivity of the terbium-containing materials is slightly higher under reducing conditions (5% H2 + 95% Ar) than in air, reaching ~ 6 10− 2 and 2.5 10− 2 S/cm at 800 C for (Yb0.8Ca0.1Tb0.1)2Ti2O7−δ and (Dy0.8Ca0.1Tb0.1)2Ti2O7−δ, respectively. In air–hydrogen–air cycles, the bulk conductivity returns to its original level in air: ~ 2 10− 2 and 1 10− 2 S/cm at 800 C in (Yb0.8Ca0.1Tb0.1)2Ti2O7−δ and (Dy0.8Ca0.1Tb0.1)2Ti2O7−δ, respectively. Exposure of (Dy0.8Ca0.1Tb0.1)2Ti2O7−δ to a flowing mixture of 5% H2 and 95% Ar for 100 h slightly reduces its conductivity: from 0.029 to 0.023 S/cm at 900 C. The cerium-containing materials (Yb0.8Ca0.1Ce0.1)2Ti2O7−δ and (Dy0.8Ca0.1Ce0.1)2Ti2O7−δ were found to be unstable under reducing conditions. The bulk conductivity of (Yb0.8Ca0.1Ce0.1)2Ti2O7−δ is practically independent on the atmosphere while the grain boundary conductivity increased from 5.6 10− 8 in air to ~ 1 10− 5 S/cm at 425 C on reducing the sample in 5%H2–Ar gas mixture. However, after two redox cycles air–5%H2–Ar–air the sintered pellet of (Yb0.8Ca0.1Ce0.1)2Ti2O7−δ fractured whereas (Dy0.8Ca0.1Ce0.1)2Ti2O7−δ degraded immediately under reducing conditions. It was observed that the size mismatch between Ln and Ln´ cations strongly affects the bulk to grain boundary conductivity ratio in (Ln0.8Ca0.1Ln′0.1)2Ti2O7−δ (Ln=Dy, Yb; Ln′=Ce, Tb) pyrochlores.
Keywords Pyrochlore; Donor doping; High-temperature conductivity; Ionic conductivity; Solid electrolyte; Electronic conductivity
Remark Available online 8 March 2012; http://dx.doi.org/10.1016/j.ssi.2012.02.009
Link
ID=161

Spark Plasma Sintering and Hot Pressing of Hetero-Doped LaNbO4

Authors Guttorm E. Syvertsen, Claude Estourns, Harald Fjeld, Reidar Haugsrud, Mari-Ann Einarsrud, Tor Grande
Source
Journal of the American Ceramic Society
Volume: 95, Issue: 5, Pages: 1563–1571
Time of Publication: 2012-05
Abstract LaNbO4/La3NbO7 and LaNbO4/LaNb3O9 cer-cer composites were prepared by impregnating Ca-doped LaNbO4 powder, synthesized by spray pyrolysis, with La- or Nb-precursor solutions. The sintering of the calcined powders was investigated by dilatometry, and dense composites were prepared by conventional sintering, hot pressing, and spark plasma sintering. The particle size of the starting powders was about 50 nm, and the average grain size of the dense materials ranged from 100 nm and upwards, depending on the sintering temperature, sintering procedure, and the phase composition. The unit cell parameters of LaNbO4 showed a finite size effect and approached the cell parameters of tetragonal LaNbO4 with decreasing crystallite size, both for the single-phase material and the composites. The minority phase (La3NbO7 or LaNb3O9) were observed as isolated grains and accumulated at triple points and not along the grain boundaries, pointing to a large dihedral angle between the phases. The calcium-solubility in the minority phases was larger than in LaNbO4, which corresponds well with previous reports. The electrical conductivity of the hetero-doped materials was similar to, or lower than, that for Ca-doped LaNbO4.
Remark Link
ID=158

50 mol% indium substituted BaTiO3: Characterization of structure and conductivity

Authors S.M.H. Rahman, C.S. Knee, I. Ahmed, S.G. Eriksson, R. Haugsrud
Source
International Journal of Hydrogen Energy
Volume: 37, Issue: 9, Pages: 7975–7982
Time of Publication: 2012-05
Abstract BaTi0.5In0.5O3−δ was prepared by solid state reaction at 1400 C. Rietveld analysis of high resolution X-ray powder diffraction data indicated phase pure as-prepared material that adopts a cubic perovskite structure with a = 4.1536(1) . Thermogravimetric analysis revealed the presence of significant levels of protons in the as-prepared material and 57% of the theoretically achievable protonation was attained on exposure to a humid environment at 185 C. After hydration the cell parameter increased to 4.1623(1) . Electrical conductivity was measured both with fixed and variable frequency ac impedance methods as a function of temperature, oxygen-, water vapour- and heavy water vapour partial pressures. In the temperature range 400–800 C a slight increase in the total conductivity with increasing oxygen partial pressure is encountered, characteristic of a contribution from p-type charge carriers. The effect of the water vapour pressure on conductivity below 600 C is much more prominent indicative of dominant proton conduction. At 300 C the total conductivity in wet O2 was estimated to be 9.30 10−5 S/cm. At T > 800 C the material is a pure oxide ion conductor.
Keywords Barium titanate; Perovskite; Brownmillerite; Proton conductivity; X-ray diffraction; Impedance spectroscopy
Remark Link
ID=157

Ion mobility, phase transitions, and conductivity of crystal phases in KF-CsF-SbF3-H2O system according to data of NMR and impedance spectroscopy

Authors V. Ya. Kavun, L. A. Zemnukhova, A. I. Ryabov, A. B. Podgorbunskii, S. V. Gnedenkov, S. L. Sinebryukhov and V. I. Sergienko
Source
Russian Journal of Electrochemistry
Volume: 48, Issue: 1, Pages: 104-110
Time of Publication: 2012-01
Abstract The methods of NMR, thermogravimetric analysis, and impedance spectroscopy were used to study ion mobility, phase transitions, and ion conductivity in crystal phases in the KF-CsF-SbF3-H2O system. Analysis of 19F NMR spectra allowed tracing the dynamics of ion movement in the fluoride sublattice under temperature variations, determining their types and temperature ranges, in which they are implemented. The observed phase transitions in potassium-cesium fluoroantimonates(III) are phase transitions to the superionic state. It is found that the predominant form of ion movement in the high-temperature modifications formed as a result of phase transitions becomes diffusion of fluoride ions. According to the results of electrophysical studies the K1−xCsx SbF4 (x ≤ 0.2) high-temperature phases are superionic. Their conductivity reaches the values of ∼10−2 to 10−3 S/cm at 463–483 K. The high-temperature phases are stabilized under cooling, which results in a significant increase in conductivity at the room temperature.
Keywords potassium-cesium tetrafluoroantimonates(III) – ion mobility – phase transitions – conductivity – NMR spectra
Remark DOI: 10.1134/S1023193512010090
Link
ID=154

Influence of Microwave-Assisted Pechini Method on La0.80Sr0.20Ga0.83Mg0.17O3–δ Ionic Conductivity

Authors S. Boldrini, C. Mortal, S. Fasolin, F. Agresti, L. Doubova, M. Fabrizio, and S. Barison
Source
Fuel Cells
Volume: 12, Issue: 1, Pages: 54–60
Time of Publication: 2012-02
Abstract With the aim of investigating the microwave influence on the electrolyte material properties, La0.80Sr0.20Ga0.83Mg0.17O2.815 was prepared by both a conventional and a microwave-assisted sol–gel Pechini method. With respect to the conventional Pechini method (hereafter SGP), the microwave assisted process (hereafter MWA-SGP) guaranteed a faster procedure, reducing the time needed to remove the excess solvents to complete the polyesterification reaction from some days to a few hours. In fact, when a MWA-SGP method was used, powders having higher phase purity were obtained. The sintering process at 1,450 C of the powders prepared by both methods yielded pellets with similar density values (≥92% of theoretical). Nevertheless, only by microwave-assisted process single-phase products were obtained and no secondary phases such as tetragonal LaSrGaO4 and LaSrGa3O7 were detected. These by-products have been demonstrated to be detrimental for conductivity. Indeed, pellets obtained by MWA-SGP method showed oxygen ionic conductivity values higher (about 30–40%) than those checked for SGP samples, thus demonstrating the important role of the microwave process on reducing time and costs and on improving the electrolyte properties.
Keywords Ionic Conductivity;IT-SOFC;Microwave Processing;(Sr, Mg)-Doped LaGaO3;Sol–Gel
Remark Link
ID=152

On the hydration of grain boundaries and bulk of proton conducting BaZr0.7Pr0.2Y0.1O3-δ

Authors Kristine Bakkemo Kostl, Anna Magras, Truls Norby
Source
International Journal of Hydrogen Energy
Volume: 37, Issue: 9, Pages: 7970–7974
Time of Publication: 2011-12
Abstract We report here for the first time bulk and grain boundary conductivities from impedance spectra of a ceramic proton conductor (BaZr0.7Pr0.2Y0.1O3-δ) taken during hydration and H/D isotope exchange transients (at 400 C). The results suggest that water moves quickly along grain boundary cores, and then interact from there with the space charge layers and, in turn, grain interiors. Hydration and H/D isotope exchange have simple monotonic effects on the bulk conductivity in line with what is expected from it being dominated by protons. The transients for grain boundary conductivity exhibit however hysteresis: During hydration, the core charge and grain boundary resistance appear to go through transient minima related to non-equilibrium distributions of defects between the core and grain interior – notably because protons diffuse faster than oxygen vacancies between the grain boundary and grain interior. At equilibrium, hydration increases the core charge and the depletion of positive charge carriers in the space charge layers. During H/D isotope exchange relatively fast hysteretic transients indicate that the space charge layers experience changes in charge carrier (D+ vs. H+) mobility as well as in D2O vs. H2O hydration thermodynamics.
Keywords BaZrO3, Pr-substituted, acceptor-doped; BaZr0.7Pr0.2Y0.1O3-δ; Proton conductivity; Grain boundaries, space charge layer; Hydration; Impedance spectroscopy
Remark Link
ID=150

Dielectric Relaxation in BaTiO3–Bi(Zn1/2Ti1/2)O3 Ceramics

Authors Natthaphon Raengthon, David P. Cann
Source
Journal of the American Ceramic Society
Volume: 95, Issue: 5, Pages: 1604–1612
Time of Publication: 2012-05
Abstract A dramatic improvement in the dielectric and electrical properties has been observed in ceramics of 0.8BaTiO3–0.2Bi(Zn1/2Ti1/2)O3 through the introduction of Ba vacancies. It possesses a high relative permittivity (εr > 1150) along with a low dielectric loss (tan δ < 0.05) that is maintained up to temperatures as high as 460C. It is also characterized by a high resistivity of 70 GΩ-cm, which remains constant up to 270C. Analysis of complex impedance (Z*) and complex electric modulus (M*) data, measured over the frequency range of 1–106 Hz, revealed a number of important findings. At high temperatures (T > 255C), a complex plane analysis of Z″ versus Z′ and the frequency dependence of Z″ suggests an electrically inhomogeneous microstructure for the stoichiometric composition. The stoichiometric composition exhibited activation energies of ~1 eV which suggests an extrinsic conduction mechanism. However, the introduction of Ba vacancies resulted in electrically homogeneous microstructure. An overlap of the Z″ and M″ peaks in the frequency domain and much larger activation energies were observed, on the order of half of the band gap, suggesting an intrinsic conduction mechanism. A more detailed analysis of the data reveals insights into the physical mechanisms underpinning the dielectric and ac conductivity.
Remark Link
ID=148

Fabrication and electrochemical properties of cathode-supported solid oxide fuel cells via slurry spin coating

Authors Min Chen, Jing-Li Luo, Karl T. Chuang, Alan R. Sanger
Source
Electrochimica Acta
Volume: 63, Pages: 277–286
Time of Publication: 2012-02
Abstract A cathode-supported SOFC consisting of LSM (La0.8Sr0.2MnO3-δ) cathode supporter, LSM-Sm0.2Ce0.8O2-δ (SDC) cathode functional layer (CFL), yttria stabilized zirconia (YSZ)/SDC bi-layered electrolyte and Ni-YSZ anode layer was fabricated by a slurry spin coating technique. The influence of the porosity in both the CFL and cathode supporter on the electrochemical properties of the cells has been investigated. It was found that properly controlling the porosity in the CFL would improve the performance of the cells using O2 in the cathode side (O2-cells), with a maximum power density (MPD) value achieving as high as 0.58 W•cm−2 at 850 C. However, this improvement is not so evident for the cells using air in the cathode side (air-cells). When increasing the porosity in the cathode-supporter, a significant increase of the power density for the air cells due to the decreasing Rconc,c(concentration polarization to the cell resistance) can be ascertained. In terms of our analysis on various electrochemical parameters, the Ract (activation polarization to the cell resistance) is assumed to be mainly responsible for the impedance arcs measured under the OCV condition, with a negligible Rconc,cvalue being able to be detected in our impedances. In this case, a significant decreasing size of the impedance arcs due to the increasing porosity in the cathode supporter would correspond to a decrease of the Ract values, which was proved to be induced by the decreasingRconc,c.
Keywords Slurry spin coating; Cathode-supported SOFC; Concentration polarization; Activation polarization; Power density
Remark Link
ID=145

The effect of cation non-stoichiometry in LaNbO4 materials

Authors Guttorm E. Syvertsen, Anna Magras, Reidar Haugsrud, Mari-Ann Einarsrud, Tor Grande
Source
International Journal of Hydrogen Energy
Volume: 37, Issue: 9, Pages: 8017–8026
Time of Publication: 2012-05
Abstract The effect of cation non-stoichiometry in LaNbO4 was investigated by impregnating nano-crystalline LaNbO4 with small amounts of La3+, Nb5+ and Ca2+ oxide precursors. The sintering properties of the modified LaNbO4 powders were investigated by dilatometry, and the microstructure and phase composition were studied by electron microscopy and X-ray diffraction. The electrical properties of the materials were studied by 4-point DC-conductivity and 2-point 4-wire AC-conductivity at elevated temperatures in controlled atmosphere. Minor variations in the cation stoichiometry were shown to have a pronounced effect on both the sintering properties as well as the electrical conductivity. Addition of CaO, which introduced secondary phases above 0.25 mol% CaO, increased the sintering temperature and improved the conductivity of the materials. La2O3- and Nb2O5-excess materials did not show large variation in the electrical conductivity relative to pure LaNbO4, while the sintering properties were strongly affected by the nominal La/Nb ratio in LaNbO4. The present findings demonstrate the sensitivity of cation non-stoichiometry in materials with limited solid solubility.
Keywords LaNbO4; Proton conductivity; Phase purity; Solid solubility
Remark Link
ID=143

Hydration and proton conductivity in LaAsO4

Authors Tor S. Bjrheim, Truls Norby and Reidar Haugsrud
Source
Journal of Materials Chemistry
Volume: 22, Issue: 4, Pages: 1652-1661
Time of Publication: 2012-04
Abstract Incorporation and transport of protonic defects have been studied in nominally undoped and 1 and 3 mol% Sr-doped LaAsO4 prepared by a co-precipitation route. AC impedance of the materials was measured as a function of temperature (1150 to 400 C), pO2 (1 to 1 10−5 atm) and pH2O (0.025 to 3 10−5 atm). The bulk conductivities generally decrease with decreasing temperature and moreover with decreasing pH2O within the whole temperature range. At the highest temperatures, a small decrease in the conductivity with decreasing pO2 was also observed. The defect structure of Sr-doped LaAsO4 appears to be dominated by oxygen vacancies in the form of pyroarsenate ions, As2O4−7, in dry atmospheres at high temperatures and by protonic defects in the form of hydrogen arsenate ions, HAsO2−4, in wet atmospheres. A significant isotope effect shows that protons contribute to the total conductivity at all temperatures under wet conditions and predominate at temperatures below [similar]850 C. The remaining contributions are attributed to oxide ions and electron holes. The extracted hydration thermodynamics are comparable to those determined for other LnXO4 (X = P, V, Nb, Ta) compounds, and the enthalpy of mobility of protons (86 5 and 88 5 kJ mol−1 for the 1 and 3 mol% doped samples, respectively) follows an apparent trend for the isostructural LaXO4 (X = P, As, V) series with the enthalpy of mobility of protons decreasing with increasing radius of the X-site cation. However, the partial proton conductivities of Sr-doped LaAsO4 are lower than those determined for acceptor doped LaPO4 and LaVO4 for which the possible reasons are discussed.
Remark Link
ID=141

Influence of Pr substitution on defects, transport, and grain boundary properties of acceptor-doped BaZrO3

Authors Anna Magras, Christian Kjlseth, Reidar Haugsrud, Truls Norby
Source
International Journal of Hydrogen Energy
Volume: 37, Issue: 9, Pages: 7962–7969
Time of Publication: 2012-05
Abstract We report on effects of partially substituting Zr with the multivalent Pr on the conductivity characteristics of acceptor (Gd) doped BaZrO3-based materials. BaZr0.6Pr0.3Gd0.1O3−δ was sintered 96% dense at 1550 C with grains of 1–4 μm. The electrical conductivity was characterised by impedance spectroscopy and EMF transport number measurements as a function of temperature and the partial pressures of oxygen and water vapour. H2O/D2O exchanges were applied to further verify proton conduction. The material is mainly a mixed proton–electron conductor: the p-type electronic conductivity is ∼0.004 and ∼0.05 S/cm in wet O2 at 500 and 900 C, respectively, while the protonic conductivity is ∼10−4 S/cm and ∼10−3 S/cm. The material is expectedly a pure proton conductor at sufficiently low temperatures and wet conditions. The specific grain boundary conductivity is essentially equal for the material with or without Pr, but the overall resistance is significantly lower for the former. We propose that replacing Pr on the Zr site reduces the grain boundary contribution due to an increased grain size after otherwise equal sintering conditions.
Keywords BaZrO3; BaPrO3; Defects and transport; Grain boundaries; Grain boundary specific conductivity
Remark Link
ID=140

Effects of A and B site acceptor doping on hydration and proton mobility of LaNbO4

Authors Morten Huse, Truls Norby, and Reidar Haugsrud
Source
International Journal of Hydrogen Energy
Volume: 37, Issue: 9, Pages: 8004–8016
Time of Publication: 2012-05
Abstract Acceptor doping of the high temperature proton conductor LaNbO4 has been studied by impedance spectroscopy in various atmospheres at 300–1100 C and by X-ray powder diffraction and scanning electron microscopy. Doping LaNbO4 on both A and B site (with Ca and Ti, respectively) resulted in a two-phase composition of LaNbO4 and LaNb3O9. This composite is interesting as the two phases make it a mixed proton and electron conductor. The electrical characterisation of Ti-doped LaNbO4 revealed mixed electronic (n- and p-type) and ionic conductivity at temperatures above approx. 750 C, while proton conductivity was dominating below this temperature under wet conditions. Ti-doping resulted in higher activation enthalpy and lower mobility of protons as compared to Ca-doping, attributed to stronger proton–acceptor association in the former case. Thermodynamic constants for hydration of associated protons and proton–acceptor association as well as mobility parameters were fitted to the experimental data and came out as , , , and , and . Neither B site doping nor A and B site co-doping showed indications of increased solubility relative to sole A site doping in LaNbO4.
Keywords LaNbO4; Ti-doped LaNbO4; Defect association; Proton mobility; Proton conductivity; Hydration thermodynamics
Remark Link
ID=139

Effects of (LaSr)(CoFeCu)O3-δ Cathodes on the Characteristics of Intermediate Temperature Solid Oxide Fuel Cells

Authors Sea-Fue Wang, Chun-Ting Yeh, Yuh-Ruey Wang, Yung-Fu Hsu
Source
Journal of Power Sources
Volume: 201, Pages: 18–25
Time of Publication: 2012-03
Abstract In this study, Cu2+ ions doped La0.6Sr0.4Co0.2Fe0.8O3−δ cathodes are prepared for use in solid oxide fuel cells (SOFCs). The maximum electrical conductivities of the La0.6Sr0.4Co0.2Fe0.7Cu0.1O3−δ (438 S cm−1) and the La0.6Sr0.4Co0.1Fe0.8Cu0.1O3−δ (340 S cm−1) discs are higher than that of the La0.6Sr0.4Co0.2Fe0.8O3−δ disc (LSCF; 81 S cm−1) sintered at 1100 C. The substitution of Cu2+ over Fe3+ leads to a higher coefficients of thermal expansion (CTE), while the replacement of Co3+ by Cu2+ results in a lower CTE. Single cells with the La0.6Sr0.4Co0.2Fe0.8O3−δ, La0.6Sr0.4Co0.2Fe0.7Cu0.1O3−δ, and La0.6Sr0.4Co0.1Fe0.8Cu0.1O3−δ cathodes operating at 650 C and 550 C show similar ohmic resistance (R0) values while the polarization resistance (RP) values of the cells with the La0.6Sr0.4Co0.2Fe0.7Cu0.1O3−δ and a0.6Sr0.4Co0.1Fe0.8Cu0.1O3−δ cathodes are slightly lower than that of the single cell with the La0.6Sr0.4Co0.2Fe0.8O3−δ cathode, indicating that the Cu2+-doped LSCF cathode exhibits a greater electrochemical catalytic activity for oxygen reduction. Maximum power densities of the cells with the La0.6Sr0.4Co0.2Fe0.8O3−δ, La0.6Sr0.4Co0.2Fe0.7Cu0.1O3−δ, and La0.6Sr0.4Co0.1Fe0.8Cu0.1O3−δ cathodes operating at 700 C read respectively 1.07, 1.15, and 1.24 W cm−2. It is evident that the doping of Cu2+ ions in LSCF is beneficial to the electrochemical performance of the cells.
Keywords Solid oxide fuel cell; cathode; cathode; impedance; Cell performance
Remark Link
ID=138

Synthesis and Enhanced Proton Conduction in a 20 mol% Ytterbium Doped Barium Zirconate Ceramic Using Zn as Sintering Aid

Authors Seikh M.H. Rahman, Istaq Ahmed, Sten G. Eriksson
Source
Applied Mechanics and Materials
Mechanical and Aerospace Engineering
Volume: 110-116 Time of Publication: 2011-10
Abstract 20% Ytterbium (III)-doped perovskite structured barium zirconate, BaZrO3, was prepared by two different synthesis routes: solid state and sol-gel routes. 2 % Zinc (II) was added as an acceptor dopant at the Zr (IV) site according to stoichiometry. It was also added as 2 % excess of the formula. The purpose of this study is to see how zinc (II) acts as a sintering aid in view of synthesis route, densification and conductivity of the material. A dense ceramic (90% of theoretical density) was achieved by the sol-gel method when stoichiometry was adjusted. Phase purity of the samples was checked by X-ray powder diffraction (XRD). Thermogravimetric analysis (TGA) and Impedance spectroscopy (IS) was used to characterize hydration and electrical conductivity respectively.The data shows that the addition of stoichiometric amounts of Zn2+ via sol-gel synthesis route promotes not only densification but also water incorporation and conductivity in comparison with the solid state route, keeping the same final sintering temperature of 1500C. For example, pre-hydrated BaZr0.78Zn0.02Yb0.2O3-δ, prepared via the sol-gel method shows total conductivity (σtot) value of 3.14*10-5 and 3.8*10-3 Scm-1, whereas for the solid state route, σtot values are 1.74*10-5 and 8.87*10-4 Scm-1 under dry Ar (heating cycle) at 300 C and 600 C, respectively.
Keywords BaZrO3, Impedance Spectroscopy, Proton Conductivity, Sintering Aid, TGA, X-Ray Diffraction (XRD)
Editor Wu Fan
Remark Online since October, 2011; DOI 10.4028/www.scientific.net/AMM.110-116.1181
Link
ID=134

Post-heat treatment pressure effect on performances of metal-supported solid oxide fuel cells fabricated by atmospheric plasma spraying

Authors Chun-Huang Tsai, Chang-sing Hwang, Chun-Liang Chang, Jen-Feng Yu, Sheng-Hui Nien
Source
Journal of Power Sources
Volume: 197, Pages: 145–153
Time of Publication: 2012-01
Abstract The nickel metal-supported cells fabricated by atmospheric plasma spraying are post-heat treated in air at 960 C for 2 h with different pressures. The current–voltage–power and AC impedance measurements show the prepared cell with an applied pressure of 450 g cm−2 in the post-heat treatment has a better electrochemical performance at test temperatures ≥ 650 C. For test temperatures < 650 C, the maximum power densities at 450 g cm−2 pressure are about the same as the maximum power densities at 1250 g cm−2 pressure. The SEM micrograph indicates that the cathode including the cathode interlayer and the cathode collector is the most porous region in the cell. AC impedance results show this cathode is the most sensitive part to the applied pressure in the post-heat treatment and the cell with 450 g cm−2 pressure has the smallest low frequency intercept R2 and the polarization resistance Rp at temperatures from 600 to 800 C. The performance durability test of the cell post-heat treated at 450 g cm−2 pressure shows a degradation rate of 0.0087 mV h−1 or 0.0026 mW h−1 at 300 mA cm−2 constant current density and 750 C test temperature.
Keywords Atmospheric plasma spray; Solid oxide fuel cells; Metal-supported; Nanostructured
Remark Link
ID=117

Structure, Water Uptake, and Electrical Conductivity of TiP2O7

Authors Vajeeston Nalini, Magnus H. Srby, Koji Amezawa, Reidar Haugsrud, Helmer Fjellvg, Truls Norby
Source
Journal of the American Ceramic Society
Volume: 94, Issue: 5, Pages: 1514–1522
Time of Publication: 2011-05
Abstract We report here on the structure of TiP2O7 and electrical properties of nominally acceptor (Sc, Fe)-doped TiP2O7 synthesized by an aqueous phosphoric acid route. Structural characterization, including studies of the high-temperature phase transition in TiP2O7, was carried out by powder X-ray and neutron diffraction. Ceramic disks were sintered by the spark plasma technique and their conductivities were characterized as a function of p(O2) and p(H2O) in the temperature range of 500–1000C by means of AC constant frequency measurements and impedance spectroscopy. As reported earlier, the acceptor doping appears not to influence the defect structure of TiP2O7 significantly. Effects of H+/D+ isotope shift were utilized to identify proton conduction. The conductivity was independent of p(O2) at 500–900C under oxidizing conditions suggesting predominantly protonic conduction at these temperatures. Under reducing atmosphere n-type conductivity contributed to the total conductivity at the higher temperatures. p(H2O) dependencies of the conductivities are interpreted in terms of a defect-chemical model involving protons and oxygen interstitials as the dominating defects. The uptake of water was studied by thermogravimetry at high p(H2O) and the thermodynamics of the hydration reaction was derived. Finally, parameters for the mobility of protons were extracted by combining the conductivity and thermogravimetry data.
Remark Link
ID=116

Microstructural characterization and electrical properties of spray pyrolyzed conventionally sintered or hot-pressed BaZrO3 and BaZr0.9Y0.1O3 − δ

Authors Paul Inge Dahl, Hilde Lea Lein, Yingda Yu, Julian Tolchard, Tor Grande, Mari-Ann Einarsrud, Christian Kjlseth, Truls Norby and Reidar Haugsrud
Source
Solid State Ionics
Volume: 182, Issue: 1, Pages: 32-40
Time of Publication: 2011-02
Abstract A spray pyrolysis route to BaZrO3 (BZ) and BaZr0.9Y0.1O2.95 (BZY) powders was developed starting from nitrate solutions. Homogeneous powders with a grain size of ~ 100 nm were achieved. A calcination of the powder was necessary to remove carbonates formed during the spray pyrolysis. Hot pressing was in comparison with conventional sintering more effective to enhance densification and suppress grain growth, and dense (> 96%) materials with homogeneous microstructure were obtained. The Y-substitution decreased the densification rate. Minor amounts of a secondary phase was observed at the grain boundary triple points of BZY, but the grain boundaries were otherwise found to be coherent and without significant secondary phase accumulation. Impedance spectroscopy vs T, pO2 and pH2O of conventionally sintered BZ and hot-pressed BZY demonstrated that the conductivity of BZ was orders of magnitude lower than compared to BZY. The conductivity of BZ displayed mixed proton and p-type electronic conduction characteristics in the grain interior which was depressed at the grain boundaries. The grain boundaries showed an additional n-type electronic conduction under reducing conditions. The conductivity characteristics were according to core-space charge layer theory. BZ seems to exhibit a larger ratio of p-type electronic to protonic conduction as compared to BZY, contrary to the prediction of simple defect chemistry.
ID=112

δ-Phase to defect fluorite (order–disorder) transition in the R2O3–MO2 (R = Sc; Tm; Lu; M = Zr; Hf) systems

Authors A.V. Shlyakhtina, D.A. Belov, S.Yu. Stefanovich, I.V. Kolbanev, O.K. Karyagina, A.V. Egorov, S.V. Savilov and L.G. Shcherbakova
Source
Materials Research Bulletin
Volume: 46, Issue: 4, Pages: 512–517
Time of Publication: 2011-04
Abstract We have studied the δ-phase to defectfluoriteF* (order–disorder) transition in the R4M3O12 (R = Sc, Tm, Lu; M = Zr, Hf) compounds. The temperature of the δ–F* phasetransition in Tm4Zr3O12 is ∼1600 C. The rate of this transition in R4Zr3O12 (R = Sc, Tm, Lu) decreases markedly with decreasing difference in ionic radius between the R3+ and Zr4+, leading to stabilization of the δ-phasesR4Zr3O12 with R = Sc and Lu at high temperatures (∼1600 C). During slow cooling (5 C/h), the high-temperature defectfluoritesF*-R2Hf2O7 (R = Tm, Lu) decompose reversibly to form the δ-phasesR4Hf3O12. Some of the materials studied exhibit microdomains formation effects, typical of the fluorite-related oxide compounds in the R2O3–MO2 (M = Ti, Zr, Hf) systems of the heavy rare earths. The high-temperature defectfluoritesF*-R4M3O12 (R = Tm, Lu; M = Zr, Hf) as a rule contain antiphase microdomains of δ-R4Zr3O12. After slow cooling (5 C/h), such microdomains are large enough for the δ-phase to be detected by X-ray diffraction. The conductivity data for R4M3O12 (R = Sc, Tm, Lu; M = Zr, Hf) and Ln2Hf2O7 (Ln = Dy, Lu) prepared by different procedures show that the rhombohedral phasesδ-R4M3O12 (R = Sc, Tm, Lu; M = Zr, Hf) are poorer conductors than the defectfluorites, with 740 C conductivity from 10−6 to 10−5 S/cm. The conductivity drops with decreasing rare-earth ionic radius and, judging from the Ea values obtained (1.04–1.37 eV), is dominated by oxygen ion transport. The highest conductivity, ∼6 10−4 S/cm at 740 C, is offered by the rapidly cooled F*-Dy2Hf2O7. In the fluorite homologous series, oxygen ion conductivity decreases in the orderdefect pyrochlore > defectfluorite > δ-phase.
Keywords Fluorite; δ-Phases R4M3O12; Pyrochlore; Order–disorder transition; Antiphase microdomains; High-temperature conductivity
Remark Link
ID=110

Proton conductivity in Sm2Sn2O7 pyrochlores

Authors K.E.J. Eurenius, E. Ahlberg and C.S. Knee
Source
Solid State Ionics
Volume: 181, Issue: 35-36, Pages: 1577-1585
Time of Publication: 2010-11
Abstract The electrical conductivity of the pyrochlore systems, Sm2Sn2O7, Sm1.92Ca0.08Sn2O7 − δ and Sm2Sn1.92Y0.08O7 − δ was studied using impedance spectroscopy under wet and dry gas (O2 and Ar) in the temperature range 150–1000 C. Enhancements of the bulk conductivity of all samples at temperatures up to ~ 550 C were observed for wet conditions consistent with significant levels of proton conduction. The presence of dissolved protons in the acceptor-doped materials, Sm1.92Ca0.08Sn2O7 − δ and Sm2Sn1.92Y0.08O7 − δ, is supported by infrared spectroscopy and thermogravimetric analysis. Proton conduction was confirmed by isotope effects under heavy water (O2/D2O and Ar/D2O). The A-site substituted sample Sm1.92Ca0.08Sn2O7 − δ yielded the highest levels of proton conduction and displayed mixed ionic and electronic conduction under dry oxidising conditions. Electron hole conduction dominates in dry oxygen for Sm2Sn1.92Y0.08O7 − δ and Sm2Sn2O7. For the A-site doped sample bulk and grain boundary conduction could be separated. The specific grain boundary conduction was calculated using the brick layer model and was found to be two orders of magnitude lower compared to the bulk conductivity. The unexpected increase in conductivity seen for the undoped sample under wet gas is discussed in the context of structural disorder and possible filling of the un-occupied anion site in the pyrochlore structure by OH-groups.
Keywords Sm2Sn2O7; Proton conductor; Pyrochlore; Oxide ion conductivity; p-type conductivity; Infra-red spectroscopy; Thermogravimetric analysis
ID=105

Scandium stabilized zirconium thin films formation by e-beam technique

Authors Darius Virbukas, Giedrius Laukaitis, Julius Dudonis, Oresta Katkauskė and Darius Milčius
Source
Solid State Ionics
Volume: 184, Issue: 1, Pages: 10–13
Time of Publication: 2011-03
Abstract Scandiumstabilizedzirconium (10ScSZ) thin ceramic films were deposited by e-beam evaporation of (ZrO2)0.90(Sc2O3)0.10 micro powder (particle size 0.5 0.7 μm). The influence of deposition rate on formed thinfilms microstructure and electrical properties was studied. 10ScSZ thinfilms were deposited on two types of different substrates: optical quartz (SiO2) and Alloy-600 (Fe–Ni–Cr) substrates. Deposition rate was changed from 2 to 16 /s to test its influence on thinfilmformation and its properties. The microstructure of formed 10ScSZ thin ceramic films was studied by X-ray diffraction (XRD) and scanning electron microscopy (SEM). Electrical parameters of formed thin ceramics were investigated in the frequency range from 0.1 Hz to 1.0 MHz (in temperature range from 473 to 873 K). The ionic conductivity of the deposited electrolyte 10ScSZ thinfilms was determined by impedance spectroscopy. It was determined that the deposition rate (in range from 2 to 16 /s) has influence on crystallite size. It increases by increasing the deposition rate from 18.4 to 26.9 nm. The XRD measurements show that the formed 10ScSZ thinfilms do not repeat the crystallographic phase of the initial evaporated powder material—it is changes from rhombohedra (initial powder) to cubic (the formed thinfilms).
Keywords Scandium stabilized zirconium (ScSZ); Ionic conductivity; Electron beam deposition; Solid oxide fuel cells (SOFC)
Remark Link
ID=94

The properties of scandium and cerium stabilized zirconium thin films formed by e-beam technique

Authors Darius Virbukas, Giedrius Laukaitis, Julius Dudonis and Darius Milčius
Source
Solid State Ionics
Volume: 188, Issue: 1, Pages: 46–49
Time of Publication: 2011-04
Abstract Scandium and ceriumstabilizedzirconium (10Sc1CeSZ) thin ceramic films were formed evaporating (ZrO2)0.89(CeO2)0.01(Sc2O3)0.10 micro powder using e-beam evaporation technique. The influence of deposition rate on formedthinfilms electrical properties and microstructure was studied. 10Sc1CeSZ thinfilms were deposited on two types of different substrates: optical quartz (SiO2) and Alloy 600 (Fe–Ni–Cr). Deposition rate was changed from 2 to 16 /s to understand its influence on thinfilm formation and other properties. The formed 10Sc1CeSZ thinfilms keep the cubic crystal structure as the initial evaporated powder material but change the main crystallographic peak from (111) to (200) for both types of substrate and used deposition rates. It was determined that the crystallites size increases from 19.0 to 24.9 nm and from 15.6 to 19.9 nm on optical quartz and Alloy 600 respectively by increasing the deposition rate (in range from 2 to 16 /s). The thinfilm density decreases by increasing the deposition rate. The ionic conductivity of 10Sc1CeSZ thinfilms was determined by impedance spectroscopy in the frequency range from 0.1 Hz to 1.0 MHz in temperature range from 473 K to 873 K. The best ionic conductivity σtot = 4.91 10− 2 Sm− 1 at 873 K temperature and the lowest value of activation energy ΔEa = 0.88 eV were found for 10Sc1CeSZ thinfilmsformed at 4 /s deposition rate.
Keywords Scandium and cerium stabilized zirconium (10Sc1CeSZ); Electron beam deposition; Solid oxide fuel cells (SOFC); Ionic conductivity
Remark Link
ID=93

Ethanol internal steam reforming in intermediate temperature solid oxide fuel cell

Authors Stefan Diethelm, Jan Van Herle
Source
Journal of Power Sources
Volume: 196, Issue: 17, Pages: 7355–7362
Time of Publication: 2011-09
Abstract This study investigates the performance of a standard Ni–YSZ anode supported cell under ethanolsteamreforming operating conditions. Therefore, the fuelcell was directly operated with a steam/ethanol mixture (3 to 1 molar). Other gas mixtures were also used for comparison to check the conversion of ethanol and of reformate gases (H2, CO) in the fuelcell. The electrochemical properties of the fuelcell fed with four different fuel compositions were characterized between 710 and 860 C by I–V and EIS measurements at OCV and under polarization. In order to elucidate the limiting processes, impedance spectra obtained with different gas compositions were compared using the derivative of the real part of the impedance with respect of the natural logarithm of the frequency. Results show that internalsteamreforming of ethanol takes place significantly on Ni–YSZ anode only above 760 C. Comparisons of results obtained with reformate gas showed that the electrochemical cell performance is dominated by the conversion of hydrogen. The conversion of CO also occurs either directly or indirectly through the water–gas shift reaction but has a significant impact on the electrochemical performance only above 760 C.
Keywords SOFC; Ni–YSZ anode; Ethanol; Internal reforming; Coking; Impedance spectroscopy
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ID=91

Proton Conductivity in Mixed B-Site Doped Perovskite Oxide BaZr0.5In0.25Yb0.25O3−delta

Authors Istaq Ahmed,1,2 Francis G. Kinyanjui,1 Seikh M. H. Rahman,1 Patrick Steegstra,3 Sten G. Eriksson,1 and Elisabet Ahlberg3
Source
J. Electrochem. Soc.
Volume: Volume 157, Issue: Issue 12, Pages: B1819-B182
Time of Publication: 2010-12
Abstract A wet chemical route was used to prepare the oxygen deficient codoped perovskite oxide BaZr0.5In0.25Yb0.25O3−. Analysis of X-ray powder diffraction data showed that the sample belongs to the cubic crystal system with space group Pmm. Dynamic thermogravimetric (TG) analysis confirmed complete filling of oxygen vacancies (V) by protonic defects (OH) during the hydration process. The proton conductivity was investigated by impedance spectroscopy. The bulk and total conductivities of prehydrated BaZr0.5In0.25Yb0.25O3− were found to be 8.510−4 and 2.210−5 S cm−1, respectively, at 300C. The total conductivity in the codoped perovskite oxide was higher compared to that of the respective single doped perovskite oxides with the same doping level. The bulk and grain-boundary mobility and diffusion coefficients of protons were calculated at 200C using impedance and TG data to obtain the conductivity and proton concentration, respectively. The high bulk diffusivity (2.310−7 cm2 s−1) was obtained which indicates that the protons are more free to move in the heavily doped matrix compared to the lightly doped systems where trapping of protons occurs.
Keywords barium compounds, proton exchange membrane fuel cells, thermal analysis, vacancies (crystal), X-ray diffraction, zirconium compounds
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ID=68

A combined conductivity and DFT study of protons in PbZrO3 and alkaline earth zirconate perovskites

Authors Tor S. Bjrheim, Akihide Kuwabara, Istaq Ahmed, Reidar Haugsrud, Svein Stlen and Truls Norby
Source
Solid State Ionics
Volume: 181, Issue: 3-4, Pages: 130-137
Time of Publication: 2010
Abstract The electrical properties of nominally undoped and 4 mol% Y-doped PbZrO3 have been investigated by AC conductivity measurements and impedance spectroscopy under various pH2O and pO2 at high temperatures. The results indicate that the defect structures are dominated by acceptors (Y dopant and/or Pb vacancies formed during synthesis). In dry atmosphere and at high temperatures, the acceptors are compensated by oxygen vacancies. These are hydrated and replaced by protonic defects (hydroxide ions on oxide ion sites) at higher pH2O and lower temperatures. In oxidizing atmospheres, a minority concentration of electron holes dominates the conductivity. At lower temperatures and in wet atmosphere, a significant protonic conductivity contribution is also observed. Based on pO2 and pH2O isotherms, a model for incorporation of protonic defects has been applied, and the standard enthalpy of hydration of oxygen vacancies in undoped PbZrO3 has been determined (− 1.07 0.13 eV). The measured total conductivities are influenced by high grain boundary resistance. Hence, the enthalpy is at the present stage assigned to the polycrystalline ceramic material as such. Rough estimates of bulk proton mobility in Y-doped PbZrO3 yield uH+0 = 17 cm2K/Vs and ΔHm,H+ = 0.93 eV. A complementary DFT study of the hydration thermodynamics of PbZrO3 and the alkaline earth zirconate perovskites AZrO3 (A = Ca, Sr, Ba) is also reported. The experimental and theoretical hydration enthalpies are compared with those of other ABO3 perovskites. Correlations between the hydration thermodynamics and other properties of the materials are discussed.
Keywords PbZrO3; CaZrO3; SrZrO3; BaZrO3; Conductivity; Proton; Proton mobility; DFT; Thermodynamics; Defects; Hydration
ID=67

Electrical conductivity and oxygen permeation properties of SrCoFeOx membranes

Authors Jay Kniep, Qinghua Yin, Izumi Kumakiri and Y.S. Lin
Source
Solid State Ionics
Volume: 180, Issue: 40, Pages: 1633-1639
Time of Publication: 2010
Abstract The total conductivity and oxygen permeation properties of dense SrCoFeOx membranes synthesized from the solid state method were studied in the temperature range of 700–900 C. The SrCoFeOx membranes consist of an intergrowth (Sr4Fe6 − xCoxO13 δ), perovskite (SrFe1 − xCoxO3 − δ), and spinel (Co3 − xFexO4) phase. SrCoFeOx exhibits n-type and p-type conduction at low and high oxygen partial pressures, respectively, and has a total conductivity of 16.5 S/cm at 900 C in air. The oxygen permeation fluxes for SrCoFeOx and SrFeCo0.5Ox membranes were measured with either an inert or carbon monoxide sweep gas. The oxygen permeation fluxes were higher through SrCoFeOx membranes than SrFeCo0.5Ox membranes and can be attributed to a difference in the amount and makeup of the perovskite phase present in each composition. The oxygen permeation fluxes with a carbon monoxide sweep gas were approximately two orders of magnitude larger than the fluxes measured with an inert sweep gas for both compositions. The large oxygen permeation fluxes observed with a carbon monoxide sweep are due to a higher driving force for oxygen transport and a reaction on the sweep side of the membrane that maintains a low oxygen partial pressure.
Keywords Mixed-conducting oxide membrane; Oxygen permeation; Strontium iron cobalt oxide
ID=64

Space–charge theory applied to the grain boundary impedance of proton conducting BaZr0.9Y0.1O3 − δ

Authors C. Kjolseth, , H. Fjeld, O. Prytz, P.I. Dahl, C. Estournes, R. Haugsrud, T. Norby
Source
Solid State Ionics
Volume: 181, Issue: 5-7, Pages: 268-275
Time of Publication: 2010
Abstract The specific grain interior and grain boundary conductivities, obtained from impedance spectroscopy and the brick layer model, are reported for BaZr0.9Y0.1O3 − δ as a function of pO2 and temperature. pO2-dependencies were indicative of dominating ionic and p-type electronic conduction for the grain interior under reducing and oxidizing conditions, respectively, while the grain boundaries showed an additional n-type electronic contribution under reducing conditions. Transmission electron microscopy revealed enrichment of Y in the grain boundary region. These findings indicate the existence of space–charge layers in the grain boundaries. A grain boundary core–space–charge layer model is therefore applied to interpret the data. Using a Mott–Schottky approximation, a Schottky barrier height of 0.5–0.6 V and an effective grain boundary width of 8–10 nm (= 2 space–charge layer thickness) is obtained at 250 C in wet oxygen. Finite-element modelling of the complex impedance over a grain boundary with a space–charge layer depletion of protons yields a distorted semicircle as observed in the impedance spectra.
Keywords BaZrO3; BaZr0.9Y0.1O3 − δ; Proton conductivity; Grain boundary resistance; Impedance spectroscopy; Space–charge layer
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