Electron-vacancy scattering in SrNbO₃ and SrTiO₃: A density functional theory study with nonequilibrium Green's functions

Oxygen vacancies are often attributed to changes in the electronic transport for perovskite oxide materials (ABO₃). Here, we use density functional theory coupled with nonequilibrium Green's functions to systematically investigate the influence of O vacancies and also A- and B-site vacancies, on the electronic transport as characterized by a scattering cross section. We consider SrNbO₃ and n-type SrTiO₃ and contrast results for bulk and thin film (slab) geometries. By varying the electron doping in SrTiO₃ we get insight into how the electron-vacancy scattering varies for different experimental conditions. We observe a significant increase in the scattering cross section (in units of square-lattice parameter a²) from ≈0.5-2.5a² per vacancy in SrNbO₃ and heavily doped SrTiO₃ to more than 9a² in SrTiO₃ with 0.02 free carriers per unit cell. Furthermore, the scattering strength of O vacancies is enhanced in TiO₂ terminated surfaces by a factor of more than 6 in lowly doped SrTiO₃ compared to other locations in slabs and bulk systems. Interestingly, we also find that Sr vacancies go from being negligible scattering centers in SrNbO₃ and heavily doped SrTiO₃, to having a large scattering cross section in weakly doped SrTiO₃. We therefore conclude that the electron-vacancy scattering in these systems is sensitive to the combination of electron concentration and vacancy location.