Structure, conductivity and redox stability of solid solution Ce1-xCaxVO4 (0 0.4125)

A-site-substituted cerium orthovanadates, Ce1-x CaxVO4, were synthesised by solid-state reactions. At room temperature, the solid solution limit in Ce1-xCaxVO4 series is at x = 0.4125. The crystal structure was analysed by X-ray diffraction and it exhibits a tetragonal zircon structure of space group I4(1)/amd with a = 7.4004 (1) and c = 6.4983 (6) angstrom for CeVO4. The UV-Visible absorption spectra indicated that the compounds have band gaps at room temperature in the range of 4.2-4.5 eV. Conductivity measurements were performed for the first time up to the calcium solid solution limit in both air and dry 5% H-2/Ar with conductivity values at 600 degrees C ranging from 0.3 to 20 mS cm(-1) in air to 3 to 30 mS cm(-1) in reducing atmosphere. In general, the conductivity of Ca-doped CeVO4 is higher in air but lower in a reducing atmosphere comparing to pure CeVO4. The H-2/air electrochemical cell measurement indicates that the conduction of sample Ce0.7Ca0.3VO4 is electronic dominant. Samples Ce0.9Ca0.1 VO4 and Ce0.8Ca0.2VO4 are redox stable at a temperature below 600 degrees C although the conductivity is not high enough to be used as an electrode for solid oxide fuel cells.