EUROPEAN CONGRESS AND EXHIBITION ON ADVANCED MATERIALS AND PROCESSES - EUROMAT 2021

LnVO4 orthovanadates attract attention as prospective materials for electrochemical applications, in particular, as redox-reversible electrode components for solid oxide fuel cells (SOFC) [1,2]. One important advantage of LnVO4-derived components of SOFC anodes is their good resistance to carbon deposition and sulphur-containing impurities which is critical for hydrocarbon-fueled SOFCs. The present work was focused on the impact of the acceptor-type substitution by calcium on the electrical transport properties of zircon-type orthovanadate PrVO4 under oxidizing conditions.
Undoped PrVO4 and calcium-substituted Pr1-xCaxVO4-δ (x = 0.02-0.20) were prepared by conventional solid state route and sintered at 1300ºC for 5h in air. The prepared materials were characterized by X-ray and neutron diffraction, SEM/EDS, thermal analysis, and measurements of electrical properties in controlled atmospheres. XRD demonstrated the formation of phase-pure solid solutions with tetragonal zircon-type structure for up to 5 at.% of calcium in Pr sublattice, while SEM/EDS suggest a lower solubility due to the presence of Ca-V-O phase impurities. Pr(Ca)VO4 ceramics showed semiconducting behavior under oxidizing conditions at 400-900ºC. Within the solubility range, doping with calcium increases the total conductivity. The ionic and electronic contributions at 700-900ºC were assessed by the modified e.m.f. technique. The electronic conductivity is p-type and decreases with decreasing p(O2). At lower temperatures, the total conductivity was found to be higher in wet atmospheres compared to dry conditions, thus implying a significant contribution of protonic transport at temperature below 550ºC. The redox behavior of PrVO4-based ceramics on isothermal cycling between air and 10%H2-N2 was studied by impedance spectroscopy, thermogravimetry and XRD analysis.