Phase transition of ferroelectrics seen with PDF

Yoneda, Yasuhiro   ; Kohara, Shinji*

Local structures of BaTiO and BiFeO perovskite ferroelectrics were investigated by X-ray pair-distribution function (PDF) analysis in wide temperature ranges. In BaTiO, the high-temperature cubic structure deformed to rhombohedral structure through three phase transitions. On the other hand, in BiFeO the high-temperature cubicstructure deformed to the rhombohedral structure through only one phase transition. The temperature evolution of the PDFs for BaTiO and BiFeO indicated that in BaTiO, the positions of the PDF peaks did not change too much excluding the temperature factor. In BiFeO the shapes of PDF peaks changed drastically at the phase transition temperature. Thus, we found two types of phase transitions in ferroelectrics. In one, the average structure changed, but local structure unchanged like BaTiO. Another is that both average and local structure changed like BiFeO.