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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
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Pure and Mn-doped La4SrTi5O17 layered perovskite as potential solid oxide fuel cell material: Structure and anodic performance

Authors Cdric Prillat-Merceroz, Pascal Roussel, Marielle Huv, Edouard Capoen, Sbastien Rosini, Patrick Glin, Rose-Nolle Vannier, Gilles H. Gauthier
Source
Journal of Power Sources
Volume: 274, Pages: 806–815
Time of Publication: 2015
Abstract Pure and 5% Mn doped layered perovskites La4SrTi5O17, members of the La4Srn-4(Ti,Mn)nO3n+2 series with n = 5, have been synthesized and investigated as anode materials for Solid Oxide Fuel Cells. The use of XRD, neutron and electron diffraction techniques allows clarifying some divergences concerning the structural characterization within the family, not only in air but also in anodic-like N2/H2(97/3) atmosphere. The electrical conductivity of both compounds is very low in air but those values increase by two orders of magnitude in diluted hydrogen. The study of catalytic properties for methane steam reforming as well as in-depth analysis of the SOFC anodic behaviour of both materials are described, for which a microstructure optimization of the electrode allows to demonstrate the potential interest of the lamellar materials upon the classical three-dimensional cubic-like LSTs.
Keywords SOFC; Anode; Layered perovskite; Titanate; Methane steam reforming; Electrochemical impedance spectroscopy
Remark doi:10.1016/j.jpowsour.2014.10.131
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Electrochemical performance and carbon deposition resistance of Ce-doped La0.7Sr0.3Fe0.5Cr0.5O3-δ anode materials for solid oxide fuel cells fed with syngas

Authors Yi-Fei Sun, Jian-Hui Li, Kart T. Chuang, Jing-Li Luo
Source
Journal of Power Sources
Volume: 254, Pages: 483–487
Time of Publication: 2015
Abstract Ce-doped La0.7Sr0.3Fe0.5Cr0.5O3-δ (Ce-LSFC) perovskite anode catalysts for solid oxide fuel cells are successfully synthesized by a modified combustion method for the first time. The pure perovskite structure without formation of CeO2 is obtained when the content of Ce ≤ 10%. Compared with La0.7Sr0.3Fe0.5Cr0.5O3-δ anode, Ce-LSFC anode not only shows much higher catalytic activity towards the oxidation of syngas with less carbon deposition, but also displays better regeneration from coking. The enhanced performance is attributed to the more available oxygen vacancies in lattice and better oxygen mobility after doping with Ce.
Keywords SOFC; Ce-doped LSFC; Perovskite
Remark doi:10.1016/j.jpowsour.2014.10.090
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Visualization of conduction pathways in a lanthanum lithium titanate superionic conductor synthesized by rapid cooling

Authors Kazuhiro Mori, Shogo Tomihira, Kenji Iwase, Toshiharu Fukunaga
Source
Solid State Ionics
Volume: 268, Issue: A, Pages: 76-81
Time of Publication: 2014
Abstract Three-dimensional structure and conduction pathways of the lithium ions in 7Li0.4La0.53TiO3 quenched with liquid nitrogen were studied using reverse Monte Carlo modeling and the bond valence sum approach using neutron diffraction data. The lithium ions were primarily located in the region between the off-center positions of the A-sites and bottlenecks defined by four coordinating oxygen ions. The bottlenecks in the predicted conduction pathways of the lithium ions were classified into three types (I, II, and III) by their size. The type II bottlenecks were the most accessible to lithium-ion migration and more than 70% of the bottlenecks were type II.
Keywords Lithium-ion conductor; Lanthanum lithium titanate; Local structure; Neutron diffraction; Reverse Monte Carlo modeling; Bond valence sum
Remark doi:10.1016/j.ssi.2014.09.030
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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
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Versatile apparatus for thermoelectric characterization of oxides at high temperatures

Authors Matthias Schrade, Harald Fjeld, Truls Norby and Terje G. Finstad
Source
Review of Scientific Instruments
Volume: 85, Pages: 103906
Time of Publication: 2014
Abstract An apparatus for measuring the Seebeck coefficient and electrical conductivity is presented and characterized. The device can be used in a wide temperature range from room temperature to 1050 C and in all common atmospheres, including oxidizing, reducing, humid, and inert. The apparatus is suitable for samples with different geometries (disk-, bar-shaped), allowing a complete thermoelectric characterization (including thermal conductivity) on a single sample. The Seebeck coefficient α can be measured in both sample directions (in-plane and cross-plane) simultaneously. Electrical conductivity is measured via the van der Pauw method. Perovskite-type CaMnO3 and the misfit cobalt oxide (Ca2CoO3) q (CoO2) are studied to demonstrate the temperature range and to investigate the variation of the electrical properties as a function of the measurement atmosphere.
Remark http://dx.doi.org/10.1063/1.4897489
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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
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Thermal Depolarization in the High-Temperature Ternary Piezoelectric System xPbTiO3–yBiScO3–zBi(Ni1/2Ti1/2)O3

Authors Troy Y. Ansell, David P. Cann, Eva Sapper and Jrgen Rdel
Source
Journal of the American Ceramic Society
Time of Publication: 2014
Abstract In the high-temperature ternary perovskite piezoelectric system xPbTiO3–yBiScO3–zBi(Ni1/2,Ti1/2)O3 (PT–BS–BNiT), the addition of bismuth to the A site and nickel to the B site leads to compositions that exhibit diffuse relaxor-like behavior. For these, depolarization temperature, not Curie point, is the critical value of temperature. Depolarization temperature (Td) is defined as the temperature at which the steepest loss in polarization occurs. This temperature is observed in poled materials through two different methods: loss tangent measurements and in situ d33. Across the ternary system, multiple dielectric anomalies occurred which was observed in dielectric tests where the dielectric peak broadens and becomes frequency dependent as BNiT content increased. For different compositions, the value of Td ranged between 275C–375C. Values for the piezoelectric coefficient increased with temperature up to d33 = 1000 pC/N during in situ d33. High temperature (up to 190C) and high field (up to 40 kV/cm) were also applied to test ferroelectric properties in these regimes.
Remark DOI: 10.1111/jace.13268
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Characterization and Modeling of La 1 − x Sr x CoO 3 − δ Solid Oxide Fuel Cell Cathodes Using Nonlinear Electrochemical Impedance Techniques

Author Timothy James McDonald
Source
Time of Publication: 2014
Remark Dissertation
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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
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Electrical conductivity and TG-DSC study of hydration of Sc-doped CaSnO3 and CaZrO3

Authors Andreas Lken, Christian Kjlseth, Reidar Haugsrud
Source
Solid State Ionics
Volume: 267, Pages: 61–67
Time of Publication: 2014
Abstract Correlations linking hydration thermodynamics to materials parameters can be of vital importance for further development of proton conducting oxides. However, the currently proposed correlations are troubled by scattering limiting their predictive power. As such, the present contribution has investigated Sc-doped CaSnO3 and CaZrO3 in an attempt to further elucidate the trends in the thermodynamics of hydration for perovskites. Conductivity and impedance spectroscopy on 5 and 10% Sc-doped CaSnO3 demonstrated that it is primarily an oxygen ion conductor with a small protonic contribution at lower temperatures (below 500 C) under wet conditions. Simultaneous thermogravimetry (TG) and differential scanning calorimetry (DSC), TG-DSC, was applied to measure the standard molar hydration enthalpy of CaSn1−xScxO3−δ and CaZr1−xScxO3−δ (x = 0.05, 0.10, 0.15 and 0.20) as a function of the Sc concentration. The hydration enthalpy becomes increasingly negative with increasing Sc substitution, which is discussed on the basis of changes in electronegativity, basicity and tolerance factor.
Keywords Defects; Protons; Hydration; Thermodynamics; Perovskites
Remark DOI: 10.1016/j.ssi.2014.09.006
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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
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Hydrogen permeability of SrCe0.7Zr0.25Ln0.05O3−δ membranes (Ln=Tm and Yb)

Authors Wen Xing, Paul Inge Dahl, Lasse Valland Roaas, Marie-Laure Fontaine, Yngve Larring, Partow P. Henriksen, Rune Bredesen
Source
Journal of Membrane Science
Volume: 473, Pages: 327–332
Time of Publication: 2015
Abstract Zr substituted acceptor doped SrCeO3 materials were synthesized by citric acid route and characterized by XRD and SEM. The hydrogen flux of the materials was measured as a function of temperature and hydrogen partial pressure on the feed side. The hydrogen permeability for SrCe0.7Zr0.25Tm0.05O3−δ and SrCe0.7Zr0.25Yb0.05O3−δ is similar under our measurement window and shows the same hydrogen partial pressure dependency. Under short circuit condition, the hydrogen permeability increased significantly by more than one order of magnitude indicating that the hydrogen transport is limited by electronic conduction under open circuit conditions. The observed data were discussed by applying defect chemistry and the conventional ambipolar transport theory. After the hydrogen permeation measurements, the indication of kinetic cation de-mixing was found by XRD analysis.
Keywords Co-substitution of B site; Hydrogen flux; Permeability; Acceptor doping; SrCeO3
Remark DOI: 10.1016/j.memsci.2014.09.027
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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
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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
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Crystal Structure and electrical properties of complex perovskite solid solutions based on (1-x) NaNbO3-xBi (Zn0.5Ti0.5) O3

Authors Sasiporn Prasertpalichat, David P. Cann
Source
Journal of Electroceramics
Time of Publication: 2014
Abstract Ceramics based on the perovskite solid solution (1-x) NaNbO3-xBi (Zn0.5Ti0.5) O3 were prepared using conventional solid state synthesis. The crystal structure, electrical, and optical properties were examined. According to diffraction data, a single perovskite phase could be identified up to the composition x = 0.09. As the Bi (Zn0.5Ti0.5) O3 content increased the crystal structure transitioned from orthorhombic to pseudocubic symmetry. Furthermore, dielectric data showed that the dielectric maximum shifted to lower temperatures with the addition of Bi (Zn0.5Ti0.5) O3. Polarization hysteresis data revealed a slim linear loop across the whole range of solid solutions. Optical data also showed a decrease in the optical band gap from 3.4 eV for pure NaNbO3 to 2.9 eV for the x = 0.09 composition. Using impedance spectroscopy, an electrically inhomogeneous microstructure was observed for compositions with increased Bi (Zn0.5Ti0.5) O3 content. Finally, the substitution of Ta on the B-site was shown to shift the dielectric maximum to temperatures as low as 100 K.
Remark DOI 10.1007/s10832-014-9953-x
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A family of oxide ion conductors based on the ferroelectric perovskite Na0.5Bi0.5TiO3

Authors Ming Li, Martha J. Pietrowski, Roger A. De Souza, Huairuo Zhang, Ian M. Reaney, Stuart N. Cook, John A. Kilner & Derek C. Sinclair
Source
Nature Materials
Volume: 13, Pages: 31-35
Time of Publication: 2014
Abstract Oxide ion conductors find important technical applications in electrochemical devices such as solid-oxide fuel cells (SOFCs), oxygen separation membranes and sensors1, 2, 3, 4, 5, 6, 7, 8, 9. Na0.5Bi0.5TiO3 (NBT) is a well-known lead-free piezoelectric material; however, it is often reported to possess high leakage conductivity that is problematic for its piezo- and ferroelectric applications10, 11, 12, 13, 14, 15. Here we report this high leakage to be oxide ion conduction due to Bi-deficiency and oxygen vacancies induced during materials processing. Mg-doping on the Ti-site increases the ionic conductivity to ~0.01 S cm−1 at 600 C, improves the electrolyte stability in reducing atmospheres and lowers the sintering temperature. This study not only demonstrates how to adjust the nominal NBT composition for dielectric-based applications, but also, more importantly, gives NBT-based materials an unexpected role as a completely new family of oxide ion conductors with potential applications in intermediate-temperature SOFCs and opens up a new direction to design oxide ion conductors in perovskite oxides.
Remark doi:10.1038/nmat3782
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Thermoelectric Properties of A-site Deficient Lanthanum Substituted Strontium Titanate

Author Thomas Emdal Loland
Source
Time of Publication: 2014
Remark Link

Grain Size Dependent Comparison of ZnO and ZnGa2O4 Semiconductors by Impedance Spectrometry

Authors Shalima Shawuti, Musa Mutlu Can, Mehmet Ali Glgn,Tezer Fırat
Source
Electrochimica Acta
Time of Publication: 2014
Abstract We investigated the electrical properties of ZnGa2O4 via AC (alternating current) Impedance Spectroscopy method comparing with ZnO reference material. Experimentally, AC electrical conductivity of ZnO and ZnGa2O4 were found to be a function of temperature and grain size; i.e., the increase in grain size of the ZnO led a decrease in room temperature conductivity from 1.35 10−7 S cm−1 to 9.9 10−8 S cm−1. The temperature dependent resistivity variation of ZnGa2O4 and ZnO were similar to each other with varied responding temperature. Likewise, the conductivity for ZnGa2O4 decrease from 2.2 10−8 S cm−1 to 3.8 10−9 S cm−1 upon an increase in grain size from ∼0.5 μm to 100 μm, accordingly. In addition, a rise in temperature caused an increase in conductivity and led to a corresponding shift in the relaxation time towards the lower values. The semicircles in Nyquist plots disappeared at temperature above 250 C and 700 C for ZnO and ZnGa2O4, respectively. The AC measurements were also correlated with the size dependent activation energies (171 meV for 0.5 μm ZnO and 1200 meV for 0.5 μm ZnGa2O4).
Keywords Activation energy; Nyquist plots; AC Impedance spectrometry; Oxide semiconductors
Remark DOI: 10.1016/j.electacta.2014.08.084
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Effect of thermobaric treatment on the structure and properties of CaCu3Ti4O12

Authors N. I. Kadyrova, Y. G. Zainulin, N. V. Mel’nikova, I. S. Ustinova, I. G. Grigorov
Source
Bulletin of the Russian Academy of Sciences: Physics
Volume: 78, Issue: 8, Pages: 719-722
Time of Publication: 2014
Abstract CaCu3Ti4O12 is prepared by means of solid-state sintering. The effect of thermobaric treatment (P = 8.0 GPa and T = 1100C) and partial replacement of titanium by vanadium on the microstructure and dielectric properties of CaCu3Ti4O12 are investigated.
Remark Link

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
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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
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Oxygen interstitial and vacancy conduction in symmetric Ln2 x Zr2 x O7 x/2 (Ln = Nd, Sm) solid solutions

Authors A. V. Shlyakhtina, D. A. Belov, A. V. Knotko, I. V. Kolbanev, A. N. Streletskii, O. K. Karyagina, L. G. Shcherbakova
Source
Inorganic Materials
Volume: 50, Issue: 10, Pages: 1035-1049
Time of Publication: 2014
Abstract We have compared (Ln2 − x Zr x )Zr2O7 + x/2 (Ln = Nd, Sm) pyrochlore-like solid solutions with interstitial oxide ion conduction and Ln2(Zr2 − x Ln x )O7 − δ (Ln = Nd, Sm) pyrochlore-like solid solutions with vacancy-mediated oxide ion conduction in the symmetric systems Nd2O3-ZrO2 (NdZrO) and Sm2O3-ZrO2 (SmZrO). We have studied their structure, microstructure, and transport properties and determined the excess oxygen content of the (Sm2 − x Zr x )Zr2O7 + x/2 (x = 0.2) material using thermal analysis and mass spectrometry in a reducing atmosphere (H2/Ar-He). The Ln2 x Zr2 x O7 x/2 (Ln = Nd, Sm) solid solutions have almost identical maximum oxygen vacancy and interstitial conductivities: (3–4) 10−3 S/cm at 750C. The lower oxygen vacancy conductivity of the Ln2(Zr2 − x Ln x )O7 − δ (Ln = Nd, Sm; 0 < x ≤ 0.3) solid solutions is due to the sharp decrease in it as a result of defect association processes, whereas the interstitial oxide ion conductivity of the (Ln2 − x Zr x )Zr2O7 + x/2 (Ln = Nd, Sm; 0.2 ≤ x < 0.48) pyrochlore-like solid solutions is essentially constant in a broad range of Ln2O3 concentrations.
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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.
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Magnetron formation of Ni/YSZ anodes of solid oxide fuel cells

Authors A. A. Solov’ev, N. S. Sochugov, I. V. Ionov, A. V. Shipilova, A. N. Koval’chuk
Source
Russian Journal of Electrochemistry
Volume: 50, Issue: 7, Pages: 647-655
Time of Publication: 2014
Abstract Physico-chemical and structural properties of nanocomposite NiO/ZrO2:Y2O3 (NiO/YSZ) films applied using the reactive magnetron deposition technique are studied for application as anodes of solid oxide fuel cells. The effect of oxygen consumption and magnetron power on the discharge parameters is determined to find the optimum conditions of reactive deposition. The conditions for deposition of NiO/YSZ films, under which the deposition rate is maximum (12 μm/h), are found and the volume content of Ni is within the range of 40–50%. Ni-YSZ films reduced in a hydrogen atmosphere at the temperature of 800C have a nanoporous structure. However, massive nickel agglomerates are formed in the course of reduction on the film surface; their amount grows at an increase in Ni content in the film. Solid oxide fuel cells with YSZ supporting electrolyte and a LaSrMnO3 cathode are manufactured to study electrochemical properties of NiO/YSZ films. It is shown that fuel cells with a nanocomposite NiO/YSZ anode applied using a magnetron sputtering technique have the maximum power density twice higher than in the case of fuel cells with an anode formed using the high-temperature sintering technique owing to a more developed gas-anode-electrolyte three-phase boundary.
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