Mixed conductivity of zircon-type Ce1-xAxVO 4±δ (A = Ca, Sr)

Abstract

Incorporation of alkaline-earth cations into the zircon-type lattice of Ce1-xAxVO4+δ (A = Ca, Sr; x = 0 - 0.2) was found to significantly increase the p-type electronic conductivity and to decrease the Seebeck coefficient, which becomes negative at x ≥ 0.1. The oxygen ionic conductivity is essentially unaffected by doping. The ion transference numbers of Cea-xAxVO4+δ in air, determined by the faradaic efficiency measurements, are in the range from 2 × 10-1 to 6 × 10-3 at 973-1223 K, increasing when temperature increases or alkaline-earth cation content decreases. The results on the partial conductivities and Seebeck coefficient suggest the presence of hyperstoichiometric oxygen, responsible for ionic transport, in the lattice of doped cerium vanadates. The activation energies for the electron-hole and ionic conduction both decrease on doping and vary in the ranges 39-45 kJ/mol and 87-112 kJ/mol, respectively.