Record Enhancement of Phase Transition Temperature Realized by H/F Substitution

Abstract

A high transition temperature (T_c ) is essential for the practical application of ferroelectrics as electronic devices under extreme thermal conditions in the aerospace, automotive, and energy industries. In recent decades, the isotope effect and strain engineering are found to effectively modulate T_c ; however, these strategies are limited to certain systems. Developing simple, universal, and practical methods to improve T_c has become an imminent challenge for expanding the applications of ferroelectrics. Here, by adopting a molecular design strategy involving H/F substitution on an organic-inorganic hybrid perovskite (1-azabicyclo[2.2.1]heptane)CdCl₃ at a T_c of 190 K, the successful synthesis of a multiaxial, ferroelectric hybrid perovskite (4-fluoro-1-azabicyclo[2.2.1]heptane)CdCl₃ is reported, which demonstrates a large spontaneous polarization of 11.2 µC cm^-2 (greater than that of polyvinylidene difluoride) and a T_c of 419 K (greater than that of BaTiO₃ ). This temperature enhancement (229 K) is the largest reported for molecular ferroelectrics, far exceeding the reported enhancements induced by the isotope effect and other techniques. This pioneering technique provides an effective and universal method for improving T_c in ferroelectrics and represents an important step toward the development of high-performance ferroelectric technology.