Electronic structure of oxygen deficient BaTiO₃

The electronic structure of oxygen deficient BaTiO₃ has been investigated by the first principles calculation. The oxygen vacancy doping in the form of isolated single vacancies does not create the localized state (i.e. trap level) in the band gap, as reported in many experimental studies. Electrons associated with the oxygen vacancy are occupied in the defect level with mainly Ti 3d e_g character in significant hybridization with O 2p state, which leads to the lowering of the defect energy level to the minimum edge of the conduction band. The resulting occupied energy band has a little dispersion indicating that BaTiO₃ becomes electrically conducting with low electron mobility. It is suggested that oxygen vacancy clustering may lead to further lowering of the defect level into the band gap.