Ferroelectricity and Piezoelectricity in Free-Standing Polycrystalline Films of Plastic Crystals

Abstract

Plastic crystals represent a unique compound class that is often encountered in molecules with globular structures. The highly symmetric cubic crystal structure of plastic crystals endows these materials with multiaxial ferroelectricity that allows a three-dimensional realignment of the polarization axes of the crystals, which cannot be achieved using conventional molecular ferroelectric crystals with low crystal symmetry. In this work, we focused our attention on malleability as another characteristic feature of plastic crystals. We have synthesized the new plastic/ferroelectric ionic crystals tetramethylammonium tetrachloroferrate(III) and tetramethylammonium bromotrichloroferrate(III), and discovered that free-standing translucent films can be easily prepared by pressing powdered samples of these compounds. The thus obtained polycrystalline films exhibit ferroelectric polarization switching and a relatively large piezoelectric response at room temperature. The ready availability of functional films demonstrates the practical utility of such plastic/ferroelectric crystals, and considering the vast variety of possible constituent cations and anions, a wide range of applications should be expected for these unique and attractive functional materials.

Piezoelectric Energy Harvesting Based on Multiaxial Ferroelectrics by Precise Molecular Design

“…Regarding research into [(CH 3 ) 3 NCH 2 X]PbI 3 (X = F, Cl, Br, I), 39 , undergo four or five phase transitions, respectively, and exhibit ferroelectric polarization switching and a relatively large piezoelectric response at room temperature. 40 Another key factor in regulating ferroelectricity should be the degree of matching between cations and anions, that is, "momentum matching theory." Specifically, the interaction between the cation and the anion acts like a rope to slow the molecular rotation during the phase transition to obtain multiaxial ferroelectricity.…”

A Molecular Crystal Shows Multiple Correlated Magnetic and Ferroelectric Switchings

“…Notably, although paraelectric-ferroelectric-paraelectric phase transitions have been observed for several molecular ferroelectrics, the distinct structural explanation offered here is novel. [51][52][53] The ferroelectric structural changes of the single crystal are associated with slight variations in the coordination configuration of the Co(II) complex cations through hydrogen-bond interactions. To gain further insight into the influence of these minute structural variations on the magnetic properties of the crystal, we performed the state-of-the-art ab initio calculations using the CASSCF/NEVPT2 approach.…”

Temperature‐Triggered Switchable Dielectric Constants in Zinc‐Based Hybrid Organic‐Inorganic Compounds: (C3H6NH2)2[ZnX4] (X = Cl and Br)

“…In molecular crystal, dipolar reorientation contributes greatly to tunable and switchable dielectric constant between high‐ and low‐dielectric state, compared with the electronic and ionic displacements . Therefore, manipulated dynamics of the dipoles is one of vital role to construct molecule‐based switchable dielectrics by motional changes of polar components between static and dynamic phases …”

“…Especially, halogenometallates including globular structures have made great progress . Intriguing property, such as dielectric transition, emerged with the structural changes via tilting and distortions of the anion tetrahedron, displacements of the metal ions, and/or disordering of the organic cations . However, the stimuli‐responsive dielectrics materials are still rarely explored.…”

“…Phase transitions in stimuli‐responsive materials arouse various physical or chemical properties such as ferroelectricity, antiferroelectricity and switchable dielectric constant . Stimuli‐responsive dielectrics materials with switchable dielectric constant have long captured much attention because they have played highly important role in acting as ultra‐low dielectrics in integrated circuits or high dielectrics in energy storage and other electric devices .…”