Halogenated carborane molecular ferroelectric crystals with high-temperature phase transition

Abstract

Molecular ferroelectrics possess spontaneous polarization, finding applications in sensors, memory devices, capacitors, among others. However, most of these materials are hybrids of organic and inorganic compounds, and few single-component pure organic ferroelectrics have been reported to have high phase transition temperatures. In this study, employing a quasi-spherical approach, five o-carborane cage molecular ferroelectric derivatives, comprising two B(9)-mono-substituted o-carboranes, B(9)–Br-o-carborane (1), and B(9)–Cl-o-carborane (2), along with three B(9,12)-di-substituted o-carboranes, B(9,12)–Br, Cl-o-carborane (3), B(9,12)–Br₂-o-carborane (4), and B(9,12)–Cl₂-o-carborane (5) were obtained by halogenation. All five compounds crystallize in the ferroelectric polar point group (2, m, mm2) and exhibit above-room-temperature ferroelectricity which are confirmed by the ferroelectric hysteresis loops and domain switching. Furthermore, the maximum transition temperature of the dibromosubstituted o-carborane molecule 4 reaches 437 K, which is 160.5 K higher compared to the precursor o-carborane. This finding offers a novel avenue for investigating organic single molecular ferroelectrics with high-temperature phase transition.