Electric field dependent polarization switching of tetramethylammonium bromotrichloroferrate(III) ferroelectric plastic crystals

Tetramethylammonium bromotrichloroferrate(III) ([N(CH3)4][FeBrCl3]) is a plastic crystal ferroelectric with small dielectric constant <20 and piezoelectric coefficient as high as 110 pC/N. Here, super-coercive hysteresis and dielectric properties under direct current (DC) bias fields up to 260 and 120 kV/cm, respectively, were studied to shed light on the polarization switching [N(CH3)4][FeBrCl3] and the related family of plastic crystal and supramolecular ferroelectrics. [N(CH3)4][FeBrCl3] exhibited peak-to-peak strains of 0.1% and saturated ferroelastic switching at fields of 170 kV/cm. Above 170 kV/cm, rates of field increase were too fast for domain switching, resulting in reduced strain rates during the switching cycle. Leakage currents had larger contributions at higher field amplitudes. This was also reflected in the switching behavior at higher frequencies, 100 Hz, in which hysteresis was asymmetric and switching incomplete. The dielectric constant and loss exhibited a butterfly-like shape during application of DC bias electric fields indicative of domain switching, but showed a small dielectric tunability of 0.038 and no signs of dielectric stiffening, with the relative permittivity from 16.9 to 17.3 at fields from 0 to 120 kV/cm. The present findings provide insight into the domain switching kinetics and dielectric properties of [N(CH3)4][FeBrCl3] that will assist with further development of plastic crystal ferroelectrics.