Ferroelasticity and Dielectric Switching in a 2D Layered Fe^II-Based Hybrid Perovskites (FCH₂CH₂NH₃)₂[Fe^IICl₄]

Hybrid organic-inorganic perovskites (HOIPs) are promising for advanced electronics. Notably, their ferroelasticity and switchable dielectric properties make them promising candidates for applications such as mechanical switches, sensors, and wearable devices. Herein, we reported a two-dimensional Fe^II-based HOIP ferroelastic material, (FCH₂CH₂NH₃)₂[Fe^IICl₄]. The compound undergoes a reversible phase transition at about 333 K, which is accompanied by stable dielectric switching properties. Structural analyses revealed that at 297 K it crystallizes in monoclinic space group P2₁/c (ferroelastic phase), while at 360 K it transforms into tetragonal space group I4/mmm (paraelastic phase), corresponding to a 4/mmmF2/m type ferroelastic transition. Polarized optical microscopy directly revealed the temperature-dependent evolution of ferroelastic domains. This work integrates ferroelasticity and reversible dielectric switching in 2D Fe^II-HOIPs, offering insights for designing multifunctional HOIPs.