Realization of High-Temperature Multiferroicity in K-Bi-Based Hybrid Double Perovskites via Interaction Engineering

Tunable organic-inorganic hybrid perovskites (OIHPs) have long been regarded as an effective platform for achieving multiferroicity. At present, extensive research has focused on regulating multiferroicity through cation modification strategies. However, the design of multiferroic materials based on halogens in the inorganic framework remains rare. Here, we report a one-dimensional van der Waals mixed-halogen double perovskite multiferroic (where ferroelectricity and ferroelasticity coexist), [RB3HQ]₂KBiCl₄Br₄ [RB3HQ = (R)-N-bromomethyl-3-hydroxyquinoline] (KBX). By introducing Br atoms, we thereby lower the energy barrier to motion during the polarity-switching process and enable stable ferroelectric ordering. Below the Curie temperature (T_c), KBX exhibits typical polarization-electric field hysteresis and a clear ferroelastic domain structure. This study reveals the crucial role of mixed-halogen regulation in promoting ferroelectric ordering. Moreover, it provides an effective experimental strategy for the design and exploration of multiferroic materials in the double perovskite system.