An Above-Room-Temperature Molecular Ferroelectric: [Cyclopentylammonium]₂CdBr₄

Abstract

Molecular ferroelectrics as alternatives to the conventional inorganic ferroelectrics have been greatly developed in past decades; many of these have been discovered and designed through various chemical means due to their structural adjustability. However, it is still a huge challenge to obtain high (above room temperature) Curie temperature (<i>T</i>_c) molecular ferroelectrics to meet the application requirements. Here, we present a new organic-inorganic hybrid molecular ferroelectric, [cyclopentylammonium]₂CdBr₄ (<b>1</b>), showing a moderate above-room-temperature <i>T</i>_c of 340.3 K. The mechanism of the ferroelectric phase transition from <i>Pnam</i> to <i>Pna</i>2₁ in <b>1</b> is ascribed to the order-disorder transition of both the organic cations and inorganic anions, affording a spontaneous polarization of 0.57 μC/cm² for the ferroelectric phase. Using piezoresponse force microscopy (PFM), we clearly observed the antiparallel 180° stripe domains and realized the polarization switching, unambiguously establishing the existence of room-temperature ferroelectricity in the thin film. These attributes make it attractive for use in flexible devices, soft robotics, biomedical devices, and other applications.