Strongly Enhanced Polarization in a Ferroelectric Crystal by Conduction-Proton Flow.

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.