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)CdCl 3 at a T c of 190 K, the successful synthesis of a multiaxial, ferroelectric hybrid perovskite (4‐fluoro‐1‐azabicyclo[2.2.1]heptane)CdCl 3 is reported, which demonstrates a large spontaneous polarization of 11.2 µ C cm −2 (greater than that of polyvinylidene difluoride) and a T c of 419 K (greater than that of BaTiO 3 ). 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.