Defects in titanates
Electronic, structural and optical properties of titanates (BaTiO3, SrTiO3, CaTiO3 and PbTiO3) containing different point defects are reviewed and discussed in the present work. The results are obtained using a quantum-chemical method based on the Hartree-Fock formalism and utilising the Large Unit Cell (LUC) and the Embedded Molecular Cluster (EMC) models. The outcomes of the computations are compared and discussed in the light of the available experimental data. The formation of Jahn-Teller (JT) polarons and bipolarons due to the presence of some point defects in the titanate crystals are found to be very important in order to understand better the behaviour of these materials. In particular, such phenomena as the non-linear photoconductivity in BaTiO3, the drastic increase in the electrical conductivity in CaTiO3 and BaTiO3 crystals, and the superconductivity in SrTiO3 could be completely or partially explained by the presence of JT polarons and different interacting mechanisms between these defects.
Keywords: titanates, quantum-chemical modelling, point defects, impurity doping, Jahn-Teller polarons, bipolarons, excitons, electronic properties, structural properties, optical properties, nanotechnology