Increasing the ferroelastic phase transition temperature of hybrid perovskites through a mixed phosphonium and ammonium cation strategy

Abstract

[(CH₃)₃PCH₂CH₂CH₃]₂(n-C₄H₉NH₃)Bi₂Br₉ (1) was obtained by a mixed organic cation strategy. The introduction of phosphonium cations increases the potential energy barrier for the motion of cations, which raises the ferroelastic phase transition temperature of 1 above room temperature, unlike the low-temperature ferroelasticity of [n-C₄H₉NH₃]₂[BiBr₅]. This provides a new idea for exploring and designing molecular ferroelastic materials with excellent performance.