High‐<i>T</i><sub>c</sub> Realization of Lead‐Free Halide Hybrid Ferroelectrics via Steric Confinement Modulation
Qin Chen, Haidong Jiang, Yipeng Fan, Zhou Li, Ye Huang, Yunpeng Yao, Shuang Chen, Chengmin Ji, Shu‐Hua Zhang, Junhua Luo
Abstract
Abstract Hybrid organic–inorganic perovskite (HOIP) ferroelectrics with high Curie temperature ( T c ), typified by the lead halide hybrid perovskite ferroelectrics, are developing rapidly owing to their maneuverable ferroelectricity at high temperatures. However, acquiring high‐ T c lead‐free HOIP ferroelectrics via rational strategy still needs development. In this study, a brand‐new program by modulating the steric confinement in a cuplike cavity to design high‐ T c bismuth‐halide ferroelectrics [H 2 mdap]BiX 5 (H 2 mdap = N ‐Methyl‐1,3‐Propanediamine, X = Cl ( 1 ), Br ( 2 ), I( 3 )) is proposed. Emphatically, the T c enhanced dramatically from 264 K of 3 to 318 K of 2 and 377 K of 1 , induced by the substitution of Br and Cl to I, accompanied with an interesting transition from second‐order phase transition (for 3 ) to the first‐order one (for 1 and 2 ). The extent of T c increase is up to 113 K, which far outweighs that of reported Pb‐halide hybrid ferroelectrics. Structural and computational analyses elucidate that this unprecedented improvement of T c is due to the higher phase transition energy barriers induced by modulating the steric confinement of cuplike cavity via halogen substitution. These results will provide new inspiration for designing high‐ T c lead‐free HOIP ferroelectrics.