Change of macroscopic and microscopic symmetry of barium titanate single crystal around Curie temperature

Using a high-quality barium titanate single crystal grown by a top-seeded solution growth method, its microscopic and macroscopic symmetries were investigated by Raman scattering measurement and polarizing microscopy, respectively. Moreover, their temperature dependences through Curie temperature were also studied. As a result, we found that the microscopic symmetry of P4mm observed at room temperature did not change through Curie temperature. On the other hand, the macroscopic symmetry on the basis of a insitu domain observation was P4mm below 133°C and Pm3m above the Curie temperature. This difference between microscopic and macroscopic symmetries above the Curie temperature suggests that the barium titanate single crystal above the Curie temperature intrinsically exhibits some disorder behavior. On the basis of the results obtained in this study, the phase transition model of barium titanate single crystal with both displacive and order-disorder behaviors was proposed.