Change of micro and macro symmetry of barium titanate single crystal around Curie temperature and its model

Using high-quality barium titanate single crystals, its microscopic and macroscopic symmetries were investigated by Raman scattering and a polarizing microscope, respectively. Their temperature dependences were also studied through Curie temperature. The microscopic symmetry of P4mm observed at 21.7°C did not change through Curie temperature. On the other hand, the macroscopic symmetry was P4mm below 133.0°C while that was Pm3m above 133.0°C. This difference between the microscopic and macroscopic symmetries above Curie temperature suggested that the barium titanate above 133.0°C has intrinsically some disordered behavior. We proposed the model, that the flipping behavior of the polar vector can be origin of the disordered behavior