Unlocking Cage‐Confined Cations Molecular Dynamics toward High‐Tc Perovskite Ferroelectrics

Cage‐confinement effect that imposes great constriction on the dynamic behaviors of guest molecules is an established platform for tailoring physical properties. Herein, the strategy of enhancing cage‐confinement effect to control molecular motion has been probed for the first time to exploit new high‐Tc ferroelectrics of 2D hybrid perovskites. By fine‐tailoring of the confined cations inside the perovskite cavities, we have successfully obtained new homologous ferroelectrics of (BA)2(MA)2Pb3Cl10 (1; BA =n‐butylamine, MA = methylamine) and (BA)2(EA)2Pb3Cl10 (2; EA = ethylamine). Intriguingly, this dynamics modulation of cage‐confined cations leads to a remarkable promotion of Curie temperature (Tc), boosting from 340 K (for 1) to 402 K (for 2). In situ solid‐state NMR spectroscopy and theoretical simulations on energy barrier confirm that the larger EA cation in 2 is subject to stronger confinement effect, of which potential energy barrier of molecular motion is ~3.5 times that of MA cation. This dynamic behavior greatly suppresses the dynamic motions of EA cation, while MA cation can easily accelerate motion and reach a fast motion limit, thus accounting for an enhancement of Tc (ΔT~62 K) in 2. The finding sheds light on the understanding of cage‐confined electric orders and the precise design of high‐performance ferroelectrics.