Stability and oxygen ionic conductivity of zircon-type Ce1-xAxVO4+δ (A = Ca, Sr)

Zircon-type Ce(1-x)A(x)VO(4+delta) (A= Ca, Sr; x = 0-0.2) are stable in air up to approximately 1300 K, whilst further heating or reducing oxygen partial pressure leads to formation of A-site deficient zircon and CeO2-delta phases. The stability boundaries of Ce(1-x)A(x)VO(4+delta) are comparable to those of vanadium dioxide and calcium orthovanadate. At oxygen pressures lower than 10(-15) atm, perovskite-type CeVO3-delta is formed. The oxygen ion transference numbers of Ce(1-x)A(x)VO(4+delta), determined by faradaic efficiency measurements in air, vary in the range from 2 x 10(-4) to 6 x 10(-3) at 973-1223 K, increasing with temperature. The oxygen ionic conductivity has activation energy of 87-112 kJ/mol and is essentially independent of A-site dopant content. Contrary to the ionic transport, p-type electronic conductivity and Seebeck coefficient of Ce(1-x)A(x)VO(4+delta) are influenced by the divalent cation concentration. The average thermal expansion coefficients of Ce(1-x)A(x)VO(4+delta), calculated from high-temperature XRD and dilatometric data in air, are (4.7-6.1) x 10(-6) K-1. (C) 2003 Elsevier Inc. All rights reserved.