Structure, conductivity and redox stability of solid solution Ce1−x Ca x VO4 (0 ≤ x ≤ 0.4125)

A-site-substituted cerium orthovanadates, Ce1−x Ca x VO4, were synthesised by solid-state reactions. At room temperature, the solid solution limit in Ce1−x Ca x VO4 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 I41/amd with a = 7.4004 (1) and c = 6.4983 (6) A 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% H2/Ar with conductivity values at 600 °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 H2/air electrochemical cell measurement indicates that the conduction of sample Ce0.7Ca0.3VO4 is electronic dominant. Samples Ce0.9Ca0.1VO4 and Ce0.8Ca0.2VO4 are redox stable at a temperature below 600 °C although the conductivity is not high enough to be used as an electrode for solid oxide fuel cells.