Impact of Acceptor-Type Substitution on Electrical Transport Properties of Zircon-Type EuVO4

Abstract

Magnesium-substituted europium vanadate ceramics, MgxEuVO4 ± (x = 0–0.5), were prepared by solidstate method and characterized by XRD, SEM/EDS, dilatometry, UV–vis spectroscopy, impedance spec-troscopy, and measurements of oxygen-ion transference numbers (to). Magnesium was found tosubstitute preferentially into vanadium sublattice of zircon-type EuVO4with limited solubility of∼5 at.%. Additions of magnesium increase slightly coefficients of thermal expansion (3.2–6.0 ppm/K at150–400◦C) and have negligible effect on the optical properties. Undoped EuVO4is predominantly anoxygen-ionic conductor with to= 0.96–0.99 at 700–900◦C under oxidizing conditions. Acceptor-type sub-stitution suppresses total conductivity and oxygen-ionic transport. The variations of electrical transportproperties are discussed in terms of interstitial oxygen diffusion in the parent EuVO4and oxygen vacancydiffusion in Mg-substituted vanadate. Humidified atmosphere has negligible impact on the electricalproperties of substituted ceramics but results in increased electrical conductivity of EuVO4indicating aprotonic contribution to the total electrical transport.