Electronic structure of (Na1/2Bi1/2)TiO3 and its solid solution with BaTiO3

The electronic structure and bonding in the (Na1/2Bi1/2)TiO3 (NBT) crystal and its solid solution with BaTiO3 (BT) are studied by first-principles loc al density calculations. For the solid solution, an ordered superstructure (Na15/32Bi15/32Ba1/16)TiO3 With 320 atoms in a large cell is proposed. The results show that both NET 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 t he increased covalent character of bonding in NET and NBT-BT crystals. The calculated OK edges for a number of related crystals are presented and comp ared. It is suggested that electron energy loss near-edge structure measure ments can be an effective tool to characterize the samples for different pi ezoelectric materials.