Electronic structure of the ferroelectric-layered perovskite bismuth titanate by ab initio calculation within density functional theory

The geometry of bismuth titanate is optimized and its electronic structure is investigated by first-principles in the framework of density functional theory. The electronic response is mainly determined by O(1) 2p states and Bi(2) 6p states, with an indirect band gap 1.87 eV. Apart from the hybridizations of Ti 3d–O 2p, there is an important hybridization between Bi and O states, which strengthens indirectly the Ti–O hybridization. The edges of the valance band and the conduction band are mainly derived from O 2p and Bi 6p states, respectively. The BTO fatigue property is attributed to the instability of the (Bi2Ti3O10)2− perovskites against oxygen vacancies. The calculated results agree well with the experimental data.