Record Enhancement of Curie Temperature in Host–Guest Inclusion Ferroelectrics

Abstract

Solid-state molecular rotor-type materials such as host–guest inclusion compounds are very desirable for the construction of molecular ferroelectrics. However, they usually have a low Curie temperature (Tc) and uniaxial nature, severely hindering their practical applications. Herein, by regulating the anion to control “momentum matching” in the crystal structure, we successfully designed a high-temperature multiaxial host–guest inclusion ferroelectric [(MeO–C6H4–NH3)(18-crown-6)][TFSA] (MeO–C6H4–NH3 = 4-methoxyanilinium, TFSA = bis(trifluoromethanesulfonyl)ammonium) with the Aizu notation of mmmFm. Compared to the parent uniaxial ferroelectric [(MeO–C6H4–NH3)(18-crown-6)][BF4] with a Tc of 127 K, the introduction of larger TFSA anions brings a lower crystal symmetry at room temperature and a higher energy barrier of molecular motions in phase transition, giving [(MeO–C6H4–NH3)(18-crown-6)][TFSA] multiaxial ferroelectricity and a high Tc up to 415 K (above that of BaTiO3). To our knowledge, such a record temperature enhancement of 288 K makes its Tc the highest among the reported crown-ether-based ferroelectrics, giving a wide working temperature range for applications in data storage, temperature sensing, actuation, and so on. This work will provide guidance and inspiration for designing high-Tc host–guest inclusion ferroelectrics.