Abstract
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)2SbX5 (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 mmmFmm2 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 (Tc) significantly increases from 348K of I-1 to 374K of Br-2. Their ferroelectricity and pyroelectricity are improved (Ps value from 1.3 to 4.0µCcm-2, pe value from 0.2 to 0.48µCcm-2K-1 for I-1 and Br-2), while their optical bandgaps increased from 2.1 to 2.7eV. 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 [SbX5]2- anions skeleton lead to PT. The semiconductor properties are determined by [SbX5]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.
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