Halide Anions Tuning of Lead-Free Perovskite-Type Ferroelectric Semiconductors with Inverse High-Temperature Symmetry Breaking

There is a noticeable gap in the literature regarding research on halogen-substitution-regulated ferroelectric semiconductors featuring multiple phase transitions. Here, a new category of 1D perovskite ferroelectrics (DFP) 2 SbX 5 (DFP + = 3,3-difluoropyrrolidium, X − = I − , Br − , abbreviated as I-1 and Br-2 ) with twophase transitions (PTs) is reported. The first low-temperature PT is a mmm F mm 2 ferroelectric PT, while the high-temperature PT is a counterintuitive inverse temperature symmetry-breaking PT. By the substitution of iodine with bromine, the Curie temperature ( T c) significantly increases from 348 K of I-1 to 374 K of Br-2 . Their ferroelectricity and pyroelectricity are improved ( P s value from 1.3 to 4.0 µC cm −2 , p e value from 0.2 to 0.48 µC cm −2 K −1 for I-1 and Br-2 ), while their optical bandgaps increased from 2.1 to 2.7 eV. A critical slowing down phenomenon is observed in the dielectric measurement of I-1 while Br-2 exhibits the ferroelastic domain. Structural and computational analyses elucidate that the order-disorder movement of cations and the distortion of the chain perovskite [SbX 5 ] 2− anions skeleton lead to PT. The semiconductor properties are determined by [SbX 5 ] 2− anions. The findings contribute to the development of ferroelectric semiconductors and materials with multiple PTs and provide materials for potential applications in the optoelectronic field.