Room‐Temperature Ferroelectricity in an Organic Cocrystal

Abstract

Ferroelectric materials exhibit switchable remanent polarization due to reversible symmetry breaking under an applied electric field. Previous research has leveraged temperature‐induced neutral‐ionic transitions in charge‐transfer (CT) cocrystals to access ferroelectrics that operate through displacement of molecules under an applied field. However, displacive ferroelectric behavior is rare in organic CT cocrystals and achieving a Curie temperature (TC) above ambient has been elusive. Here a cocrystal between acenaphthene and 2,3,5,6‐tetrafluoro‐7,7,8,8‐tetracyanoquinodimethane is presented that shows switchable remanent polarization at room temperature (TC=68 °C). Raman spectroscopy, X‐ray diffraction, and solid‐state NMR spectroscopy indicate the ferroelectric behavior is facilitated by acenaphthene (AN) rotation, deviating from conventional design strategies for CT ferroelectrics. These findings highlight the relevance of non‐CT interactions in the design of displacive ferroelectric cocrystals.Switchable remanent polarization at room temperature is displayed by the organic charge‐transfer cocrystal AN‐F4TCNQ. The ferroelectric Curie temperature was measured at 68 °C by differential scanning calorimetry, prompting further electronic and structural characterization of AN‐F4TCNQ which revealed that dynamic motion of acenaphthene (AN) contributes to the high‐temperature polarization switching.