Hydrogen-bonded organic molecular ferroelectrics/antiferroelectrics

Approximately one-third of organic molecular ferroelectrics and antiferroelectrics are hydrogen-bonded (prototropic, acid–base supramolecular, and zwitterionic) crystals of the proton-transfer type. The synergistic interplay of the intermolecular proton dynamics and switchable π-bond dipoles promotes the polarization and thermal stability, as exemplified by the above-room-temperature ferroelectric croconic acid. Highly polarizable antiferroelectric counterparts are also in the focus, from the viewpoint of the high-density and high-efficiency electrostatic energy storage and the giant electrostriction. A structural assessment using a database is noted as the methodology hidden behind many of the latest successful developments. Theoretical investigations reproduce well the experimental results, providing the feedback to improve design principles and strategies for realizing high electric polarizations. Besides the π-electron molecular ferroelectrics, the latest discovery of molecular rotational ferroelectric crystals (including plastic/ferroelectric crystals) may bring about breakthrough in material design strategies that can be used to overcome the bottlenecks inherent to the organic system.