2026-09-18 九州大学
(参考図１) 今回報告したNa2MnN(CN)4・3.25H2Oの結晶構造と強誘電ヒステリシス。
＜関連情報＞
- https://www.kyushu-u.ac.jp/ja/researches/view/1574
- https://pubs.acs.org/jacsat/article-abstract/doi/10.1021/jacs.6c12413/5434523/Multidirectional-Colossal-Polarization-in-a
長距離イオン変位による中心対称結晶における多方向巨大分極 Multidirectional Colossal Polarization in a Centrosymmetric Crystal via Long-Range Ion Displacement
Yuxin Shi;Junichi Yanagisawa;Tomoya Namiki;Fumiya Kobayashi;Makoto Tadokoro;Yuta Tsuji;Naoki Ogiwara;Benjamin Le Ouay;Masaaki Ohba;Ryo Ohtani
Journal of the American Chemical Society Published:September 21, 2026
DOI:https://doi.org/10.1021/jacs.6c12413
Abstract
Ferroelectrics exhibit spontaneous polarization and are highly functional materials that are widely used in various devices. However, the design of conventional ferroelectric compounds is largely limited to noncentrosymmetric, polar structures. Herein, we demonstrate that colossal polarization occurs by long-range ion displacement even in the nonpolar proton conductor Na2MnN(CN)4·3.25H2O (1·H2O). This compound crystallized in the nonpolar I2/a space group but exhibited extremely large polarization owing to conducting protons, as confirmed by ferroelectric hysteresis and thermally stimulated depolarization current measurements. A remanent polarization of 438 mC cm–2 was achieved along the [010] direction of single crystals at 298 K under 80% relative humidity at 0.01 Hz. The polarization values are associated with proton conduction, largely depending on the frequency, temperature, and humidity. Single-crystal characterization revealed that polarization emerges in multiple directions and that the polarization magnitude and frequency-response vary depending on the crystallographic axis. These results indicate that the polarization phenomena, driven by long-range ion displacements, are strongly governed by the anisotropic one-dimensional framework of 1·H2O. Moreover, the functionality of this system is underpinned by hydrogen bonds between the inorganic skeleton and water, as confirmed by experiments employing H2O and D2O. This study demonstrates that ionic conductors can exhibit polar functionalities without breaking the inversion symmetry.
