Electronic structure of (Na½Bi½)TiO3 and its solid solution with BaTiO3

The electronic structure and bonding in the (Na15/32Bi½)TiO3 (NBT) crystal and its solid solution with BaTiO3 (BT) are studied by first-principles local density calculations. For the solid solution. an ordered superstructure (Na15/32Bi15/32Ba1/16)TiO3 with 320 atoms in a large celi is proposed. The results show that both NBT and NBT-BT are semiconductors with a band gap of about 1 eV. NBT is shown to be a harder crystal than PbTiO3 and PbZrO3 by having a larger calculated bulk modulus. This can be attributed partly to the increased covalent character of bonding in NBT and NBT-BT crystals. The calculated O K edges for a number of related crystals are presented and compared. It is suggested that electron energy loss near-edge structure measurements can be an effective tool to characterize the samples for different piezoelectric materials.