Origin of the Diverse Behavior of Oxygen Vacancies in ABO3 Perovskites: A Symmetry Based Analysis

Using band symmetry analysis and density functional theory calculations, we reveal the origin of why oxygen vacancy (V _O) energy levels are shallow in some ABO ₃ perovskites, such as SrTiO ₃, but are deep in some others, such as LaAlO ₃. We show that this diverse behavior can be explained by the symmetry of the perovskite structure and the location (A or B site) of the metal atoms with low d orbital energies, such as Ti and La atoms. When the conduction band minimum (CBM) is an antibonding Γ ₁₂ state, which is usually associated with the metal atom with low d orbital energies at the A site (e.g., LaAlO ₃), then the V _O energy levels are deep inside the gap. Otherwise, if the CBM is the nonbonding Γ25 ^′ state, which is usually associated with metal atoms with low d orbital energies at the B site (e.g., SrTiO ₃), then the V _O energy levels are shallow and often above the CBM. The V _O energy level is also deep for some uncommon ABO ₃ perovskite materials that possess a low s orbital, or large-size cations, and an antibonding Γ ₁ state CBM, such as ZnTiO ₃. Our results, therefore, provide guidelines for designing ABO ₃ perovskite materials with desired functional behaviors.