20031: Mashiyama-Kawamura-Magome-Kubota

Journal: Journal of Korean Physical Society, Supple. Issue Vol.42, pp.S1026-S1029

Title: Displacive Character of the Cubic-Tetragonal Transition in CH₃NH₃PbX₃

Authors: ^*H. MASHIYAMA and Y. KAWAMURA
Affiliation: Faculty of Science, Yamaguchi University, Yamaguchi 753-8512, Japan

Authors: E. MAGOME
Affiliation: Graduate School of Science, Hiroshima University, Higashi-Hiroshima 739-8526, Japan

Authors: Y. KUBOTA
Affiliation: Faculty of Science, Osaka Women's University, Sakai 590-8512, Japan

The cubic-tetragonal phase transition in CH₃NH₃PbBr₃ is investigated from the detailed structural analysis. The powder diffraction profiles, obtained with using a Debye-Scherrer camera installed at SPring-8, are analyzed by a Rietveld pattern fitting program. The lattice parameters change as if a second order transition takes place, with accompanying superlattice reflections. In the cubic phase, the structure could be refined either by the displacive model or by the order-disorder model. But the latter model is not fully consistent throughout the transition. The former model gives the rotating angle of the PbBr6 octahedron, which increases monotonically with decreasing temperature. The angle is considered to be an order parameter, and the displacive character of the phase transition is concluded in CH₃NH₃PbBr₃ and CH₃NH₃PbI₃.