The formation energies and electronic structure of lattice vacancies, antisite defects, and lanthanum impurities in NaTaO3 were investigated using first-principles calculations based on density-functional theory. The Na antisite and the Ta vacancy, which were both multiple acceptors, were energetically favorable under O-rich conditions, whereas the O vacancy, which was a double donor, was preferred under O-poor conditions. The Ta antisite was a quadruple donor but its high formation energy renders it unlikely to be stable under the thermal equilibrium other than p-type and O-poor conditions. In La-doped NaTaO3, substitutional La at the Na site was likely to form as a double donor under O-poor conditions. It was expected to generate carrier electrons except for heavily doped cases where compensation by acceptor-like La at the Ta site, as well as the native acceptors, was significant. For all the native defects and La impurities, no localized one-electron states were found in the band gap, which was consistent with the shallow donor/acceptor behavior determined using the formation energies.

First-Principles Study of Native Defects and Lanthanum Impurities in NaTaO3. M.Choi, F.Oba, I.Tanaka: Physical Review B, 2008, 78[1], 014115 (8pp)