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Thin-film La0.58Sr0.4Co0.2Fe0.8O3-δ (LSCF58428) exhibits high oxygen permeability due to its high ionic and electronic conductivity. In order to increase the oxygen flux, a thin-film membrane on a structural substrate is beneficial. Different Ni-based alloys were studied as potential substrate materials. The chemical compositions and thermal expansion coefficients of Nibased alloys were measured in this study. LSCF58428 layers were screen printed on Ni-based alloys and cofired at a high temperature in air. Microstructural and elemental analyses of samples were conducted using a scanning electron microscope and energy-dispersive X-ray spectroscope. X-ray diffraction was used to investigate the phase compositions. The Ni-based alloy, MCrAlY (with M = Ni, Co), with a high Al content showed better chemical compatibility with perovskite material at high temperatures than other Ni-based alloys. A reaction occurred between Sr in the perovskite and the alumina-based surface layer on MCrAlY. However, the reaction zone was found to be stable in mid-term annealing at 800°C in air. Hence, it is expected that this reaction will not prevent application as an oxygen transport membrane. Three different cofiring atmospheres were investigated. Air was found to be the only possible cofiring atmosphere. [ABSTRACT FROM AUTHOR]

In an effort to improve the performance of heat engines at high temperatures, advanced surface coatings have been developed from complex perovskites. Materials of Ba(Mg1/3Ta2/3)O3 and La(Al1/4Mg1/2Ta1/4)O3 composition were synthesized and applied as ceramic topcoats of thermal barrier coating (TBC) systems by atmospheric plasma spraying (APS) in single layer and in double-layer combination with conventional yttria stabilized zirconia (YSZ). Microstructural and phase analyses reveal that plasma spraying of complex perovskites is accompanied with the formation of vertical crack networks and secondary oxide phases which influence the failure mechanism of the TBCs. The low value of fracture toughness for the complex perovskites and the thermally grown oxide at the topcoat-bondcoat interface of the TBCs are, however, the major factors which lead to the coating failure on thermal cycling at about 1250 °C. [ABSTRACT FROM AUTHOR]

Perovskite-type SrZrO3 was investigated as an alternative to yttria-stabilized zirconia (YSZ) material for thermal barrier coating (TBC) applications. Three phase transformations (orthorhombic↔pseudo-tetragonal↔tetragonal↔cubic) were found only by heat capacity measurement, whereas the phase transformation from orthorhombic to pseudo-tetragonal was found in thermal expansion measurements. The thermal expansion coefficients (TECs) of SrZrO3 coatings were at least 4.5% larger than YSZ coatings up to 1200°C. Mechanical properties (Young's modulus, hardness, and fracture toughness) of dense SrZrO3 showed lower Young's modulus, hardness, and comparable fracture toughness with respect to YSZ. The “steady-state” sintering rate of a SrZrO3 coating at 1200°C was 1.04 × 10−9 s−1, which was less than half that of YSZ coating at 1200°C. Plasma-sprayed coatings were produced and characterized. Thermal cycling with a gas burner showed that at operating temperatures ∼1250°C the cycling lifetime of SrZrO3/YSZ double-layer coating (DLC) was more than twice as long as SrZrO3 coating and comparable to YSZ coating. However, at operating temperatures >1300°C, the cycling lifetime of SrZrO3/YSZ DLC was comparable to the optimized YSZ coating, indicating SrZrO3 might be a promising material for TBC applications at higher temperatures compared with YSZ. [ABSTRACT FROM AUTHOR]

Abstract: Nonstoichiometric yittrium-substituted SrTiO3 samples with a nominal composition of Sr x Y0.07TiO3± δ (x =0.87–1.01) and Sr0.895Y0.07Ti x O3 − δ (x =1.00–1.20) were prepared and investigated. Phase impurities were found in samples with too high A-site or B-site deficiency. The electrical properties of the samples sintered in reducting atmosphere at different temperatures were analyzed with a view to their potential use as anode materials for solid oxide fuel cells (SOFCs). The redox properties of selected samples were investigated in detail. Samples with small A-site deficiency were considered to be the best candidates for SOFC anode materials. [Copyright &y& Elsevier]

Abstract: This paper provides a short overview on the different aspects of SOFC materials, especially of new cathode materials, ranging from considerations of material properties to long-term phenomena after cell operation. Special emphasis is laid on the reproducible manufacturing of cathode microstructures, which has to be optimised for each individual composition or powder quality. If this is not performed a comparison of various cathode materials can be misleading. The microstructure can be tailored by varying the sintering conditions, which results in different particle sizes. Besides the improvement of power density, the long-term stability of cathodes is discussed in more detail. For (La,Sr)(Co,Fe)O3 (LSCF) cathodes, the predominant factor determining voltage losses during cell operation is the temperature. The mechanism responsible for voltage deterioration is a slow decomposition of the LSCF perovskite due to partial de-mixing of strontium. [Copyright &y& Elsevier]

Abstract: The oxygen uptake and release of La1−xSrxCo1−yFeyO3−δ (x=0.2, 0.4; y=0, 0.8, 1) perovskite powders was examined with temperature-programmed techniques. In addition to the commonly used temperature-programmed reduction (TPR), temperature-programmed oxidation (TPO) was used to examine oxygen adsorption on the perovskites that had previously been partially reduced. While perovskite reduction started slowly at an offset temperature of about 300 °C, the re-oxidation already started below 100 °C resulting in a distinct re-oxidation peak. The measured oxygen stoichiometry changes were in the range of δ=0.03–0.19. For the re-oxidation process, surface-controlled kinetics was assumed, allowing the application of conventional temperature-programmed desorption (TPD) procedures to determine the activation energy of the adsorption process. Simulation of the peak profiles confirmed the predominant surface kinetics. The determined activation energies were in the range of 0.46–0.63 eV. For the measurements presented here, the demands made on preparation and experimental equipment are much lower than for other surface exchange characterisation techniques and allow a pre-selection of interesting perovskite materials for use in solid oxide fuel cells or as exhaust catalysts. [Copyright &y& Elsevier]

Abstract: Perovskite Ba(Mg1/3Ta2/3)O3, BMT has promising bulk properties (thermal conductivity ~2W/m-K and coefficient of thermal expansion ~11×10−6/K at 1473K) for thermal barrier coating (TBC) applications at high temperature. However, during atmospheric plasma spraying (APS), such material was found to lose constituents due to the differences of vapor pressures resulting to non-stoichiometric composition of deposited coatings. To investigate the extent of phase decomposition at spray distance and varying electric arc current, different feedstock powders were plasma sprayed into water and collected for chemical, microstructural and phase analyses. When the electric arc current was decreased from 500A to 300A, the decomposition of the powders was reduced and the microstructure of the deposited coatings was improved. The thermal cycling lifetime of the deposited coatings at ~1250°C surface temperature is also higher. [Copyright &y& Elsevier]

Abstract: Perovskites resulting from discrete changes in composition within the quasi-ternary system La0.8Sr0.2MnO3−δ –La0.8Sr0.2CuO2.4+δ –La0.8Sr0.2FeO3−δ were investigated under constant experimental conditions with the objective of obtaining an overview of the variation of the properties relevant for possible future applications. Nineteen nominal perovskite compositions within this system were systematically selected and synthesized under identical conditions by the Pechini method. The experimental data obtained on quantitative chemical analysis, powder X-ray diffraction, electrical conductivity and thermal expansion are presented collectively for the first time to facilitate comparisons. The formation and distribution of the different crystallographic phases at 950°C within this quasi-ternary system are shown. The DC electrical conductivity is strongly influenced by the Cu content and increases up to 276Scm−1 for La0.8Sr0.2CuO2.4+δ . The thermal expansion is dominated by the Cu/Mn ratio and is almost independent of the Fe content. [Copyright &y& Elsevier]

Abstract: The properties and the applicability of iron- and cobalt-containing perovskites were evaluated as cathodes for solid oxide fuel cells (SOFCs) in comparison to state-of-the-art manganite-based perovskites. The materials examined were La1−x−y Sr x Co0.2Fe0.8O3− δ (x =0.2 and 0.4; y =0−0.05), La0.8Sr0.2FeO3− δ , La0.7Ba0.3Co0.2Fe0.8O3− δ and Ce0.05Sr0.95Co0.2Fe0.8O3− δ . The main emphasis was placed on the electrochemical properties of the materials, which were investigated on planar anode-supported SOFCs with 8 mol% yttria-stabilised zirconia (8YSZ) electrolytes. An interlayer of the composition Ce0.8Gd0.2O2− δ was placed between the electrolyte and the cathode to prevent undesired chemical reactions between the materials. The sintering temperatures of the cathodes were adapted for each of the materials to obtain similar microstructures. In comparison to the SOFCs with state-of-the-art manganite-based cathodes, SOFCs with La1− x − y Sr x Co0.2Fe0.8O3− δ cathodes achieved much higher current densities. Small A-site deficiency and high strontium content had a particularly positive effect on cell performance. The measured current densities of cells with these cathodes were as high as 1.76 A/cm2 at 800 °C and 0.7 V, which is about twice the current density of cells with LSM/YSZ cathodes. SOFCs with La0.58Sr0.4Co0.2Fe0.8O3− δ cathodes have been operated for more than 5000 h in endurance tests with a degradation of 1.0–1.5% per 1000 h. [Copyright &y& Elsevier]

The continuing development of new materials suitable for solid oxide fuel cells operating at about 650–800 °C is of great interest in recent days. The present investigation deals with the development of a perovskite composition–LaNi0.6Fe0.4O3 (LNF)–prepared following two combustion synthesis routes: citrate-gel (LNC) and urea (LNU). The powders were sintered over a wide temperature range (900–1400 °C) and sintering behavior for LNC and LNU was compared. The thermal expansion coefficient (TEC), electrical and microstructural characteristics of LNF was thoroughly investigated. Electrical conductivities were found to be one and a half times higher than that of most commonly used cathode material, La(Sr)MnO3. Moreover, the TEC value of LNF was found to be ≈11.4×10-6 K-1 at 800 °C. The study opens up a possibility of using LNF as a promising cell component for SOFC. [Copyright &y& Elsevier]