First principles study on intrinsic vacancies in cubic and orthorhombic CaTiO₃

The structural relaxations and the formation energies of intrinsic defects in cubic and orthorhombic CaTiO₃ were investigated by a first principles projector-augmented wave method. It was found that cations and oxygen vacancies in both phases cause extra levels near the valence band maximum and the conduction band minimum, respectively, and the Ti-vacancy induced level in orthorhombic CaTiO₃ is closer to the valence band maximum than that in cubic CaTiO₃. Among the neutral defect species, including neutral isolated vacancy, partial Schottky, and full Schottky, it was found that the V_ca^2- + V_o²⁺ and V_o ⁰ are the most preferable defect species for orthorhombic CaTiO ₃ under reduction and oxidization conditions, respectively, whereas the V_ca^2- + V_o²⁺ partial Schottky is always stable in any atmosphere in cubic CaTiO₃. As compared to cubic CaTiO₃, it was found that orthorhombic CaTiO₃ shows higher defect formation energies.