2025-03-25 東京大学,高輝度光科学研究センター
＜関連情報＞
- https://www.k.u-tokyo.ac.jp/information/category/press/11498.html
- https://pubs.acs.org/doi/abs/10.1021/jacs.5c00886
非パイロエレクトリックなジャイロイド型有機金属骨格における圧電転移 Piezoelectric Transition in a Nonpyroelectric Gyroidal Metal–Organic Framework
Shunsuke Kitou,Hajime Ishikawa,Yusuke Tokunaga,Masato Ueno,Hiroshi Sawa,Yuiga Nakamura,Yuto Kinoshita,Tatsuya Miyamoto,Hiroshi Okamoto,Koichi Kindo,and Taka-hisa Arima
Journal of the American Chemical Society Published: March 24, 2025
DOI:https://doi.org/10.1021/jacs.5c00886
Abstract
Among the thirty-two crystallographic point groups, 432 is the only one that lacks an inversion center but does not exhibit piezoelectricity. A gyroidal structure belongs to point group 432 and shows characteristic physical properties attributed to its distinctive strong isotropic network. Here, we investigate a gyroidal cobalt oxalate metal–organic framework (MOF) with disordered orientations of SO4 tetrahedra. Synchrotron X-ray diffraction experiments using a single crystal reveal a cubic-to-cubic structural phase transition at TS = 120 K. This transition involves a change in the point group from nonpiezoelectric 432 to piezoelectric 23. The symmetry change arises from the ordering of distorted SO4 molecules, leading to a three-dimensional helical arrangement of electric dipole moments. Furthermore, pyroelectric current measurements using polycrystalline pellet samples reveal that electric polarization emerges below TS depending on the magnitude of the pelletizing pressure, demonstrating piezoelectricity. The gyroidal MOF offers an opportunity to explore unique dielectric properties induced by the helical ordering of molecules and structural flexibility.
