Oxide-ion conductivity optimization in BiVO4 scheelite by an acceptor doping strategy

Abstract

BiVO₄ scheelite is one of the few tetrahedra-based structures able to display vacancy-mediated oxide-ion conduction upon the use of an acceptor-doping strategy, leading to oxide-ion migration. In order to modulate the ionic migration process, it is of utmost importance to understand the different parameters affecting it. Here we review phase formation, oxygen vacancy stabilization, and migration for a wide variety of acceptor metal dopants in scheelite BiVO₄. Among them, Ca²⁺-doped materials present the widest solid-solution range, leading to optimized oxide-ion conductivities at moderately high temperatures (σ_b: ∼10⁻³ S cm⁻¹ at 500 °C), mainly as a result of their smaller size mismatch with Bi³⁺ and lower oxygen vacancy defect energy. The results gathered herein provide a useful guide for designing new oxide-ion conductors and tailoring oxide conductivity through the proper selection of doping agents according to several criteria, such as the oxygen defect formation energy, atom size mismatch, polarizability, and bond-dissociation energy with oxygen.