SPECIFICITY OF SYNTHESIS AND ELECTRICAL CONDUCTIVITY OF DENSITY CERAMIC OF La_1-xSr_xScO_3-α PROTON CONDUCTING OXIDES

The paper deals with synthesis and studies the materials with high ionic conductivity on the basis of which the various electrochemical devices are created: gas sensors, electrolyzers, devices for dosed supply of hydrogen and water vapor, etc. Interest in the study of the physicochemical properties of oxide proton conductors is due to the phenomenon of proton transfer in a solid body when hydrogen is not a structural unit of the compound. The LaScO₃ based materials are considered promising because of the high bulk conductivity at low temperature, chemical stability and mechanical strength in comparison with the well-known proton electrolytes based on cerates and zirconates of alkaline-earth elements. A comparative analysis of the properties of the proton solid electrolyte La_1-xSr_xScO_3-α (x = 0.05, 0.10) synthesized by various methods is carried out. A version of the combustion method without the use of nitrates as initial materials leading to the production of ceramics with a density of not less than 98% with respect to the theoretical was developed. Comprehensive qualitative and quantitative study was carried out by X-ray phase analysis, scanning electron microscopy, X-ray fluorescence and atomic emission spectroscopy at various stages of synthesis. The structural parameters of the La_0.9Sr_0.1ScO_3–α oxide is refined using the method of X-ray diffraction full-profile Rietveld analysis. Thermal expansion and electrical conductivity were studied as a function of the temperature and humidity of the gas phase for La_1-xSr_xScO_3-α (x = 0.05, 0.10) materials of different densities in oxidizing and reducing atmospheres. The composition of the atmosphere (dry and wet air, wet H₂) is found out to have little effect on thermal expansion below 600°C. The separation of the bulk and grain boundary conductivities by the impedance method is carried out. Both conductivities are proven to have the same activation energy for materials with a density of 94-98% relative to the theoretical one. The high porosity of the materials (30%) adversely affects the total conductivity, while the bulk conductivity is almost not reduced. The bridging model based on semicoherent boundaries that explain the low grain boundaries conductivity for proton electrolytes with a low-symmetry lattice was discussed. The data obtained from this work may be of interest to specialists in the field of hydrogen energy, electrochemistry, materials science and development of technology for electrochemical devices: sensors, power sources, fuel cells.

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