Large Phase-Transition Temperature Enhancement Achieved in a Layered Lead Iodide Hybrid Crystal by H/F Substitution
Jia-Qi Gan, Zhe‐Kun Xu, Tian Gan, Yan Qin, Zhong‐Xia Wang
Abstract
Organic–inorganic hybrid metal halides with structural flexibility and solution processability have been widely investigated for different application scenarios. However, the effective construction of phase-transition materials with a high phase-transition temperature ( T tr ) for potential practical applications remains a great challenge, and reports on the regulation of T tr with significant enhancement have been rare. In this manuscript, we have realized a large T tr increase of 148 K in a layered hybrid lead iodide crystal (4-FTMBA) 4 Pb 3 I 10 (4-FTMBA = 4-fluoro- N,N,N -trimethylbenzenaminium) by the H/F substitution strategy. Compared to the parent (TMBA) 4 Pb 3 I 10 (TMBA = N,N,N -trimethylbenzenaminium), H/F substitution preserves the structural framework and crystal symmetry in (4-FTMBA) 4 Pb 3 I 10 . The introduction of heavier fluorine will significantly increase the motion barrier for the order–disorder transition, resulting in the remarkably improved T tr . Temperature-dependent crystal structures, Raman spectra, and dielectric analyses well support the phase-transition behavior. In addition, evident thermochromism with a tunable direct band gap in (4-FTMBA) 4 Pb 3 I 10 has been observed using UV–vis spectra. To the best of our knowledge, the achieved T tr enhancement of 148 K by H/F substitution is the highest among the organic–inorganic hybrid lead halide phase-transition materials. This finding would greatly inspire the rational design of functional materials with high performance.