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Development of Temperature - Stable Relaxor Dielectrics for High Energy Density Capacitor Applications

Author Connor S. McCue
Source
Time of Publication: 2016
Remark THESIS
Link

Magnetron-Sputtered YSZ and CGO Electrolytes for SOFC

Authors A.A. Solovyev, A.V. Shipilova, I.V. Ionov, A.N. Kovalchuk, S.V. Rabotkin, and V.O. Oskirko
Source
Journal of Electronic Materials
Volume: 45, Issue: 8, Pages: 3921-3928
Time of Publication: 2016
Solid oxide fuel cell, CGO, YSZ, bilayer electrolyte, magnetron sputtering, pulse electron-beam treatment
Remark Link

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
Link

Enhanced bulk conductivity of A-site divalent acceptor-doped non-stoichiometric sodium bismuth titanate

Author Solid State Ionics
Source
Fan Yang, Patrick Wu, Derek C. Sinclair
Time of Publication: 2016
Abstract Bismuth-deficient sodium bismuth titanate (nominally Na0.5Bi0.49TiO2.985, NB0.49T) is a good oxide-ion conductor. Here we report the influence of A-site divalent ions, M2 + = Ca2 +, Sr2 + and Ba2 +, on the electrical properties of NB0.49T. A-site divalent doping for Bi3 + enhances the bulk (grain) conductivity by ~ one order of magnitude without changing the conduction mechanism, which is attributed to an increase in the oxygen vacancy concentration based on the doping mechanism Bi3 + + ½ O2 − → M2 +. Among these three dopants, Sr2 + is the most effective in increasing the bulk conductivity due to a combination of its smaller mismatch in ion size with Bi3 +, its intermediate polarisability and lower bond strength to oxygen compared to Ca2 + and Ba2 +. Doping strategies for further improvements to bulk conductivity of NBT materials are discussed based on these results. Comparison with other oxide-ion conductors and initial stability test under reducing atmosphere show the doped non-stoichiometric NBT materials are promising for low and intermediate temperature applications.
Keywords Sodium bismuth titanate; Oxide-ion conductors; Doping; Non-stoichiometry
Remark http://dx.doi.org/10.1016/j.ssi.2016.09.016
Link

Effect of high pressures and temperatures on the structure and properties of CaCu3Ti4O12

Authors N. I. Kadyrova, N. V. Mel’nikova, I. S. Ustinova, Yu. G. Zainulin
Source
Inorganic Materials
Volume: 52, Issue: 10, Pages: 1051–1054
Time of Publication: 2016
Abstract We have prepared ceramic CaCu3Ti4O12 samples by solid-state reaction and investigated the effect of high-pressure/high-temperature processing (p = 8.0 GPa, t = 1100C) on the structure and electrical properties of CaCu3Ti4O12.
Keywords High pressures and temperatures, microstructure, dielectric properties, CaCu3Ti4O12
Remark DOI: 10.1134/S0020168516100083
Link

Evaluation of La0.75Sr0.25Cr0.5Mn0.5O3 protective coating on ferritic stainless steel interconnect for SOFC application

Authors R.K. Lenka, P.K. Patro, Jyothi Sharma, T. Mahata, P.K. Sinha
Source
International Journal of Hydrogen Energy
Time of Publication: 2016
Abstract Ferritic stainless steel (SS) interconnect used for intermediate temperature solid oxide fuel cell has issues associated with the growth of oxide scale on the surface and evaporation of chromium species to the cathode leading to increase in polarization resistance and hence, overall cell resistance. Protective coating is essentially applied over the SS surface to restrict the above phenomena. In the present investigation, strontium doped lanthanum manganese chromite (LSCM) of composition La0.75Sr0.25Cr0.5Mn0.5O3 has been explored as a possible protective coating material on ferritic SS interconnect surface. For this application, fine LSCM powder was synthesized by solution polymerization method. Terpineol based slurry of LSCM was formulated and used for coating on ferritic SS surface by screen printing. LSCM coated ferritic SS was exposed to moist oxygen at 800 C for 300 h and area specific resistance (ASR) of the coating was found to be as low as 2.0 mΩ cm2 after exposure. Microstructure of LSCM coating and the chromium oxide film was investigated using SEM and EDS. The results indicate that LSCM can form an effective protective coating on ferritic stainless steel for SOFC interconnect application.
Keywords Interconnect; Protective coating; LSCM; SOFC
Remark http://dx.doi.org/10.1016/j.ijhydene.2016.08.143
Link

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
Link

Insights into the enhancement of oxygen mass transport properties of strontium-doped lanthanum manganite interface-dominated thin films

Authors F. Chiabrera, A. Morata, M. Pacios, A. Tarancn
Source
Solid State Ionics
Time of Publication: 2016
Abstract Strontium-doped lanthanum manganite thin films were deposited by pulsed laser deposition on yttria-stabilized zirconia single crystals for a comprehensive electrochemical characterization of the material acting as a cathode. A physically-meaningful electrical model was employed to fit the electrochemical impedance spectroscopy results in order to extract the main oxygen mass transport parameters as a function of the temperature and oxygen partial pressure. The oxygen diffusion and surface exchange coefficients extracted from the analysis showed several orders of magnitude of enhancement with respect to the bulk values reported in the literature and an unexpectedly low dependence with the oxygen partial pressure. Different observations were combined to propose a mechanism for the enhanced incorporation of oxygen in interface-dominated thin films mainly based on the high concentration of oxygen vacancies expected in the grain boundaries.
Remark http://dx.doi.org/10.1016/j.ssi.2016.08.009
Link

Formation of solid solutions in the CdSe–PbSe system under the action of high pressures and temperatures

Authors A. Yu. Chufarov, N. V. Melnikova, N. V. Zarubina, A. N. Ermakov, E. G. Vovkotrub, L. N. Maskaeva, V. F. Markov, Yu. G. Zainulin
Source
Russian Journal of Inorganic Chemistry
Volume: 61, Issue: 8, Pages: 1013–1018
Time of Publication: 2016
Abstract A method was proposed for producing solid solutions in the CdSe–PbSe systems, which is based on heat and high pressure treatment. X-ray powder diffraction analysis showed the formation of substitutional solid solutions CdxPb1–xSe with the NaCl structure, which contained 20, 40, 60, and 80 mol % cadmium selenide. The solid solutions were characterized by scanning electron microscopy, impedance spectroscopy, gas pycnometry, and Raman spectroscopy.
Remark DOI: 10.1134/S0036023616080052
Link

Comparison of characteristics of solid oxide fuel cells with YSZ and CGO film solid electrolytes formed using magnetron sputtering technique

Authors A. A. Solov’ev, A. V. Shipilova, A. N. Koval’chuk, I. V. Ionov, S. V. Rabotkin
Source
Russian Journal of Electrochemistry
Volume: 52, Issue: 7, Pages: 662–668
Time of Publication: 2016
Abstract The work describes the methods of manufacturing single cells of solid oxide fuel cell (SOFC) with thin–film YSZ and CGO electrolytes and also with the bilayer YSZ/CGO electrolyte. Formation of YSZ and CGO films on the supporting NiO–YSZ anode of SOFC was carried out using the combined electron–ionic–plasma deposition technique. The microstructure and phase composition of the formed coatings are studied and also comparative analysis of electrochemical characteristics of single fuel cells with different electrolytes is performed. It is shown that the maximum power density of 1.35 W/cm2 at the temperature of 800C is obtained for the cell with bilayer YSZ/CGO electrolyte. However, the highest performance at lower working temperatures (650–700C) is characteristic for the fuel cell with single–layer CGO electrolyte; its power density is 600–650 mW/cm2.
Keywords Solid oxide fuel cell, CGO, YSZ, bilayer electrolyte, magnetron sputtering, pulsed electron–beam treatment
Remark DOI: 10.1134/S102319351607017X
Link

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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Tin–Zinc oxide composite ceramics for selective CO sensing

Authors Paul Chesler, Cristian Hornoiu, Susana Mihaiu, Cornel Munteanu, Mariuca Gartner
Source
Ceramics International
Time of Publication: 2016
Abstract Composite metal oxide gas sensors were intensely studied over the past years having superior performance over their individual oxide components in detecting hazardous gases. A series of pellets with variable amounts of SnO2 (0–50 mol%) was prepared using wet homogenization of the component oxides leading to the composite tin-zinc ceramic system formation. The annealing temperature was set to 1100 C. The samples containing 2.5 mol% SnO2 and 50 mol% SnO2 were annealed also at 1300 C, in order to observe/to investigate the influence of the sintering behaviour on CO detection. The sensor materials were morphologically characterized by scanning electron microscopy (SEM). The increase in the SnO2 amount in the composite ceramic system leads to higher sample porosity and an improved sensitivity to CO. It was found that SnO2 (50 mol%) - ZnO (50 mol%) sample exhibits excellent sensing response, at a working temperature of 500 C, for 5 ppm of CO, with a fast response time of approximately 60 s and an average recovery time of 15 min. Sensor selectivity was tested using cross-response to CO, methane and propane. The results indicated that the SnO2 (50 mol%)-ZnO (50 mol%) ceramic compound may be used for selective CO sensing applications.
Keywords SnO2–ZnO; Composites; Sensors; Selective detection of CO
Remark doi:10.1016/j.ceramint.2016.07.102
Link

Synthesis and electrical properties of new perovskite-like AMn3V4O12 (A = Ca, Ce, and Sm) compounds

Authors N. I. Kadyrova, Yu. G. Zaynulin, A. P. Tyutyunnik, N. V. Melnikova, A. A. Mirzorakhimov
Source
Bulletin of the Russian Academy of Sciences: Physics
Volume: 80, Issue: 6, Pages: 620–623
Time of Publication: 2016
Abstract AMn3V4O12 (A = Ca, Ce, and Sm) compounds with a perovskite structure are synthesized at high pressures and temperatures. The crystalline structure of these compounds (space group Im3Z = 2) is determined via X-ray analysis. If ions in the A sublattice are changed in the order Ca2+–Sm3+–Ce3+, the valence is redistributed from Ca2+Mn32+V44+O12 to Sm3+Mn32+V43.75+O12, and to Ce3+Mn32+V43.75+O12. The temperature dependences of the electrical resistivity are studied.
Remark Link

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
Link

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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Structural, textural, surface chemistry and sensing properties of mesoporous Pr, Zn modified SnO2–TiO2 powder composites

Authors I. Dascalu, D. Culita, J.M. Calderon-Moreno, P. Osiceanu, C. Hornoiu, M. Anastasescu, S. Somacescu, M. Gartner
Source
Ceramics International
Volume: 43, Issue: 13, Pages: 14992–14998
Time of Publication: 2016
Abstract Mesoporous Zn and Pr modified SnO2-TiO2 mixed powders (Sn:Ti:Zn:Pr contents 60:20:15:5) have been prepared by a modified sol–gel method involving Tripropylamine (TPA) as chelating agent, TritonX100 as template and Polyvinylpyrrolidone as dispersant and stabilizer, respectively. The obtained gels have been dried at different temperatures and calcined in air at 600 and 800 C, respectively. Phase identification of the synthesized samples and their evolution with the calcination temperature has been performed by X-ray diffraction. N2 adsorption/desorption isotherms were found to be characteristic for mesoporous materials, showing relatively low values for the specific surface area (15–32 m2 g−1) and nanometric sized pores. In case of the sample calcined at 800 C, a bimodal pore size distribution can be observed, with maxima at 20 and 60 nm. SEM results demonstrate a porous nanocrystalline morphology stable up to 800 C. The surface chemistry investigated by XPS reveals the presence of the elements on the surface as well as the oxidation states for the detected elements. At 800 C a diffusion process of Sn from surface to the subsurface/bulk region accompanied by a segregation of Ti and Zn to the surface is noticed, while Pr content is unchanged. The sensing properties of the prepared powders for CO detection have been tested in the range of 250–2000 ppm and working temperatures of 227–477 C.
Keywords SnO2; TiO2; Sol–gel; Mesoporous materials; CO detection
Remark doi:10.1016/j.ceramint.2016.06.146
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New promising NASICON material as solid electrolyte for sodium-ion batteries: Correlation between composition, crystal structure and ionic conductivity of Na3 + xSc2SixP3 − xO12

Authors M. Guin, F. Tietz, O. Guillon
Source
Solid State Ionics
Volume: 293, Pages: 18–26
Time of Publication: 2016
Abstract In the search for novel sodium-ion conductors to be used in batteries for grid application, the thoroughly studied class of NASICON materials is of great interest due to compositional diversity and high ionic conductivity. The solid solution Na3 + xSc2(SiO4)x(PO4)3 − x with 0.05 ≤ x ≤ 0.8 was investigated for the first time. The various compositions were synthesized by solid state reaction and their crystallographic and electrical properties were measured. As a result, one of the best sodium-conductive NASICON materials to date was obtained for x = 0.4 (σNa,Total = 6.9 10− 4 S cm− 1 at 25 C). Furthermore, the importance of the sodium concentration and size of lattice parameters on the ionic conductivity were investigated. The bulk ionic conductivity was correlated with the structural parameters along the conduction pathway of the sodium ions and confirm the key influence of the interatomic Na–O distances on sodium ion transport.
Keywords Ionic conductivity; NASICON; Sodium; Scandium; Solid electrolyte; Battery
Remark doi:10.1016/j.ssi.2016.06.005
Link

Effect of Nb Doping on Hydration and Conductivity of La27W5O55.5−δ

Authors Cao, Y., Duan, N., Jian, L., Evans, A. and Haugsrud, R.
Source
J. Am. Ceram. Soc.
Time of Publication: 2016
Abstract Hydration properties and electrical characteristics of the high-temperature proton conductor La27(W0.85Nb0.15)5O55.5−δ are investigated by means of thermogravimetry, impedance spectroscopy, and the electromotive force (EMF) method as a function of temperature, water vapor, and oxygen partial pressures, as well as isotope exchange measurements in order to elucidate the mechanism and thermodynamics of protons formation and transport. The highest proton conductivity, 1.3 10-3 S/cm, is achieved at 700C in wet O2. Proton self-diffusion coefficients are estimated from thermogravimetric measurements of hydration and conductivity data. Comparison of the conductivity characteristics between nominally pure and Nb-substituted materials reveals that the ionic conductivity increases and the activation energy decreases with Nb doping. These differences are discussed to reflect changes in the structure promoting ionic transport rather than changing the concentration of defects to any large extent.
Keywords Lanthanum tungstate; proton concentration; proton conductivity; H/D isotope effect
Remark doi:10.1111/jace.14346
Link

Synthesis, characterization and performance of robust poison-resistant ultrathin film yttria stabilized zirconia – nickel anodes for application in solid electrolyte fuel cells

Authors F.J. Garcia-Garcia, F. Yubero, J.P. Espins, A.R. Gonzlez-Elipe, R.M. Lambert
Source
Journal of Power Sources
Volume: 324, Pages: 679–686
Time of Publication: 2016
Abstract We report on the synthesis of undoped ∼5 μm YSZ-Ni porous thin films prepared by reactive pulsed DC magnetron sputtering at an oblique angle of incidence. Pre-calcination of the amorphous unmodified precursor layers followed by reduction produces a film consisting of uniformly distributed tilted columnar aggregates having extensive three-phase boundaries and favorable gas diffusion characteristics. Similarly prepared films doped with 1.2 at.% Au are also porous and contain highly dispersed gold present as Ni-Au alloy particles whose surfaces are strongly enriched with Au. With hydrogen as fuel, the performance of the undoped thin film anodes is comparable to that of 10–20 times thicker typical commercial anodes. With a 1:1 steam/carbon feed, the un-doped anode cell current rapidly falls to zero after 60 h. In striking contrast, the initial performance of the Au-doped anode is much higher and remains unaffected after 170 h. Under deliberately harsh conditions the performance of the Au-doped anodes decreases progressively, almost certainly due to carbon deposition. Even so, the cell maintains some activity after 3 days operation in dramatic contrast with the un-doped anode, which stops working after only three hours of use. The implications and possible practical application of these findings are discussed.
Keywords Magnetron sputtering; Oblique angle deposition; Thin film anodes; Carbon-tolerant; SOFC
Remark doi:10.1016/j.jpowsour.2016.05.124
Link

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
Link

Thin film YSZ-based limiting current-type oxygen and humidity sensor on thermally oxidized silicon substrates

Author Shunsuke Akasaka
Source
Sensors and Actuators B: Chemical
Volume: 236, Pages: 499–505
Time of Publication: 2016
Abstract In this paper, we propose a thin film yttria-stabilized-zirconia (YSZ)-based limiting current-type oxygen and humidity sensor. These sensors were fabricated from layers of thin films on thermally oxidized silicon substrates, with the intention of installing such sensors onto microheaters. Sputtered porous Pt cathode are situated beneath the YSZ films, and are designed to provide a gas diffusion layer as well as function as electrodes. The porous Pt layer exhibits good performance as a gas diffusion layer because of its small pore size. Optimized YSZ sputtering growth conditions result in in-plane densification without the presence of cracks. The temperature dependence of the oxygen sensor’s level of limiting current was T −0.5. This result was attributed to the shrinkage of the extremely small pores in the gas diffusion layer. Between 450 and 550 C, following the application of a voltage of 1.1 V, the time response measurements show a rapid response of a few seconds. The oxygen concentration and water vapor pressure correspond to the level of the limiting current at 1.1 V and 1.8 V, respectively.
Keywords Yttria-stabilized-zirconia; Limiting current; Oxygen sensor; Humidity sensor; Thin film; Silicon substrate
Remark doi:10.1016/j.snb.2016.06.025
Link

Conduction Mechanisms in BaTiO3–Bi(Zn1/2Ti1/2)O3 Ceramics

Authors Kumar, N., Patterson, E. A., Frmling, T. and Cann, D. P.
Source
J. Am. Ceram. Soc.
Time of Publication: 2016
Abstract Polycrystalline BaTiO3–Bi(Zn1/2Ti1/2)O3 (BT–BZT) ceramics have superior dielectric properties for high-temperature and high-energy density applications as compared to the existing materials. While it has been shown that the addition of BZT to BT leads to an improvement in resistivity by two orders of magnitude, in this study impedance spectroscopy is used to demonstrate a novel change in conduction mechanism. While nominally undoped BT exhibits extrinsic-like p-type conduction, it is reported that BT–BZT ceramics exhibit intrinsic n-type conduction using atmosphere-dependent conductivity measurements. Annealing studies and Seebeck measurements were performed and confirmed this result. For BT, resistivity values were higher for samples annealed in nitrogen as compared to oxygen, whereas the opposite responses were observed for BZT-containing solid solutions. This suggests a fundamental change in the defect equilibrium conditions upon the addition of BZT to the solid solution that lowered the carrier concentration and changed the sign of the majority charge carrier. This is then also linked to the observed improvement in resistivity in BT–BZT ceramics as compared to undoped BT.
Remark doi:10.1111/jace.14313
Link

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
Link

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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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
Link
norecs.com

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