Oxygen vacancy diffusion in bulk SrTiO₃ from density functional theory calculations

Point defects and their diffusion contribute significantly to the properties of perovskite materials. However, even for the prototypical case of oxygen vacancies in SrTiO₃ (STO), the predictions of oxygen vacancy activity vary widely. Here we present a comprehensive and systematic study of the diffusion barriers in bulk STO. Using density functional theory (DFT), we assess the role of different supercell sizes, density functionals, and charge states. Our results show that vacancy-induced octahedral rotations, which are limited by the boundary conditions of the supercell, can significantly affect the computed oxygen vacancy diffusion energy barrier. In addition, we find that the diffusion energy barrier of a charged oxygen vacancy is lower than that of a neutral one. This difference is magnified in small supercells. We demonstrate that with increasing supercell size, the effects of the oxygen vacancy charge state and the type of DFT exchange and correlation functional diminish, and all DFT predicted migration energy barriers asymptote to a range of 0.39-0.49 eV, which is smaller than the reported experimental values. This work provides important insights and guidance that should be considered for investigations of point defect diffusion in perovskite materials and in oxide superlattices.