The Soft Molecular Polycrystalline Ferroelectric Realized by the Fluorination Effect

Abstract

For a century ferroelectricity has attracted widespread interest from science and industry. Inorganic ferroelectric ceramics have dominated multibillion dollar industries of electronic ceramics, ranging from nonvolatile memories to piezoelectric sonar or ultrasonic transducers, whose polarization can be reoriented in multiple directions so that they can be used in the ceramic and thin-film forms. However, the realization of macroscopic ferroelectricity in the polycrystalline form is challenging for molecular ferroelectrics. In pursuit of low-cost, biocompatible, and mechanically flexible alternatives, the development of multiaxial molecular ferroelectrics is imminent. Here, from quinuclidinium perrhenate, we applied fluorine substitution to successfully design a multiaxial molecular ferroelectric, 3-fluoroquinuclidinium perrhenate ([3-F-Q]­ReO4), whose macroscopic ferroelectricity can be realized in both powder compaction and thin-film forms. The fluorination effect not only increases the intrinsic polarization but also reduces the coercive field strength. More importantly, it is also, as far as we know, the softest of all known molecular ferroelectrics, whose low Vickers hardness of 10.5 HV is comparable with that in poly­(vinylidene difluoride) (PVDF) but almost 2 orders of magnitude lower than that in BaTiO3. These attributes make it an ideal candidate for flexible and wearable devices and biomechanical applications.

Hybrid Optical-Electrical Perovskite Can Be a Ferroelastic Semiconductor

“…[27][28][29][30][31][32][33][34][35][36][37] Based on this nature, sensor, switch and so on can be designed that can enrich and facilitate our daily life. [38][39][40][41][42][43][44][45] In conclusion, the discovery and design of new molecular ferroelastics is a pressing research topic.…”

H/F substitution for advanced molecular ferroelectrics

“…In addition, the molecular ferroelectric family was extended through H/F substitution. For instance, the first zinc halide ABX 3 ferroelectric (TMFM)ZnCl 3 [43] cations [16,40,50,51]. These outstanding developments are highly encouraging and validate that the H/F substitution is a legitimate strategy for the rational design of molecular ferroelectrics with unique properties.…”

“…First, because the F atom has the largest electronegativity, the fluorinated compounds can achieve enhancement in the strength of their dipole moment and further facilitate their ferroelectricity. For example, [3-F-Q]ReO 4 (3-F-Q = 3-fluoro-quinuclidinium) has been reported as the softest multiaxial molecular ferroelectric as far as we know, exhibiting a large remanent polarization (P r ) of 6.0 μC/cm 2 in the powder compaction form and the smallest Vickers hardness of 10.5 HV among molecular ferroelectrics (Figure 3A) [50]. It should be highlighted that H/F substitution not only increases the intrinsic polarization but also reduces the coercive field strength.…”

Metal ion modulation triggers dielectric double switching and green fluorescence in A2MX4-type compounds

“…In previous reports, researchers have modified spherical ions to achieve high phase transition temperature and other excellent properties. [38][39][40][41][42][43][44][45] Xiong et al 46 designed high-temperature multi-axial molecular ferroelectrics [3-oxoquinuclidinium]ClO 4 by introducing oriented hydrogen bonding interactions in molecular modifications through spherical molecular R-group substitution. In addition, some OIH materials exhibit fascinating optical properties, making it possible to integrate the different properties of multiple physical channels in one single device.…”