Molecular Disorder Induces Unusual Phase Transition in a Potential 2D Chiral Ferroelectric Perovskite.

Abstract

Two-dimensional (2D) hybrid halide perovskites with single chiral and ferroelectricity together with various structural phase transitions provide the possibility for them to have more diverse functional properties. Here, we present a 2D chiral hybrid halide perovskite ferroelectric, [C 6 H 5 (CH 2 ) 4 NH 3 ] 2 CdCl 4 ( 4PBA-CdCl 4 , 4PBA = 4-Phenylbutylamine), which experiences two continuous phase transitions from centrosymmetric triclinic P \xa0 to polar chiral monoclinic P 2 and then to another centrosymmetric tetragonal P 4 /mmm with increasing temperature, accompanied by symmetry breaking, due to the prominent octahedral distortion and disorder transformation of organic 4PBA cations. Under polar chiral phase, 4PBA-CdCl 4 exhibits a significant CD signal and a moderate ferroelectric polarization of 0.35 μC/cm 2 . In addition, 4PBA-CdCl 4 occupies a wide band gap of 4.376 eV and is chiefly contributed by inorganic CdCl 6 octahedron. This finding offers an alternative pathway for designing new phase transitions and related physical properties in hybrid halide perovskites and other hybrid crystals.