Structural Study on Cubic-Tetragonal Transition of CH₃NH₃PbI₃

抄録

The cubic-tetragonal phase transition of CH₃NH₃PbI₃ was investigated by single crystal X-ray diffractometry. The crystal structure was refined at five temperatures in the teragonal phase. The PbI₆ octahedron rorates around the c-axis alternatively to construct the SrTiO₃-type tetragonal structure. A methylammonium ion is partially orderd; 24 disordered states in the cubic phase are reduced to 8. With decreasing temperature, the rotation angle of the octahedron increases monotonically, which indicates it is an order parameter of the cubic-tetragonal transition.