Acquiring High-T_C Layered Metal Halide Ferroelectrics via Cage-Confined Ethylamine Rotators

Two-dimensional (2D) organic-inorganic hybrid perovskite (OIHP) ferroelectrics have attracted widespread interest in the field of optoelectronics due to the combination of excellent semiconducting and ferroelectric properties. The Curie temperature (T_C ), below which ferroelectricity exists, is a crucial parameter for ferroelectrics. However, the lack of research on T_C tuning of 2D OIHP ferroelectrics hinders their further progress. Here, through incorporating ethylammonium (EA) as cage-confined rotators, we obtained two 2D OIHP ferroelectrics, (IBA)₂ (EA)Pb₂ Br₇ (2L; IBA=isobutylammonium), and (IBA)₂ (EA)₂ Pb₃ Br₁₀ (3L). Intriguingly, T_C is successfully tuned from 326 K (2L) to 370 K (3L) with increasing layer thickness. Structural and computational analyses suggest that the improvement of T_C is due to the higher phase-transition energy barrier triggered by the cage-confined EA rotators with increased layer thickness. This work suggests that EA is an effective "cage-confined rotator" to rationally design high-T_C 2D OIHP ferroelectrics.