Mechanistic insights into the origin of the oxygen migration barrier

Abstract

Oxygen ion conductors require high temperatures to exhibit the high ion conductivity needed for practical use. In this work, we related oxygen vacancy formation energy and migration barrier to the electronic structure of perovskites using ab initio simulations. The vacancy formation energy increases with the increasing energy penalty for transferring electrons from oxygen to the highest filled metal states. On the other hand, the migration barrier increases with larger electronic energy penalty for screening the charge that accumulates around the oxygen vacancy. Bringing localized filled electronic states associated with the oxygen vacancy closer to the conduction band or increasing the metal–oxygen band overlap can decrease charge accumulation in the oxygen vacancy and reduce the migration barrier. By investigating the changes in the electronic structure during oxygen migration, the critical role of increasing the charge screening capability of the host lattice local environment in decreasing the migration barrier was further highlighted. Our findings provide new insights into lowering the migration barrier in oxygen ion conductors and trends towards accelerating their discovery.