Strongly Enhanced Polarization in a Ferroelectric Crystal by Conduction-Proton Flow
Junichi Yanagisawa, Takuya Aoyama, Kotaro Fujii, Masatomo Yashima, Yoshiyuki Inaguma, Akihide Kuwabara, Kazuki Shitara, Benjamin Le Ouay, Shinya Hayami, Masaaki Ohba, Ryo Ohtani
Abstract
Ion conductors comprising noncentrosymmetric frameworks have emerged as new functional materials. However, strongly correlated polarity functionality and ion transport have not been achieved. Herein, we report a ferroelectric proton conductor, K 2 MnN(CN) 4 ·H 2 O ( 1·H 2 O ), exhibiting the strong correlation between its polar skeleton and conductive ions that generate anomalous ferroelectricity via the proton-bias phenomenon. The application of an electric field of ±1 kV/cm (0.1 Hz) on 1·H 2 O at 298 K produced the ferroelectricity (polarization = 1.5 × 10 4 μC/cm 2 ), which was enhanced by the ferroelectric-skeleton-trapped conductive protons. Furthermore, the strong polarity–proton transport coupling of 1·H 2 O induced a proton-rectification-like directional ion-conductive behavior that could be adjusted by the magnitude and direction of DC electric fields. Moreover, 1·H 2 O exhibited reversible polarity switching between the polar 1·H 2 O and its dehydrated form, 1, with a centrosymmetric structure comprising an order–disorder-type transition of the nitrido-bridged chains.