Lead-free hybrid two-dimensional double perovskite with switchable dielectric phase transition

Molecular dielectric switches constitute a type of intelligent materials that are highly coveted for their distinctive advantages of switchable dielectric responses, lightweight, and mechanical flexibility. Two-dimensional (2D) hybrid perovskites have demonstrated excellent promise for assembling dielectric switches, in which the dynamic motions of organic moieties afford driving force to trigger switchable dielectric phase transition. Here, we successfully assembled a new lead-free hybrid double perovskite, (CHA)4CuBiBr8 (1, CHA = cyclohexylammonium), adopting a typical 2D structural motif, which shows dielectric anisotropy and bistable behaviors during the reversible phase transition near Tc = 378 K (the Curie temperature). That is, its dielectric constants could be switched and tuned between high-dielectric and low-dielectric states. Structure analyses reveal that the ordered-disordered transformation of the organic CHA+ moiety and distortion of inorganic framework account for its phase transition. This result will stimulate further exploration of molecular dielectric switches in this 2D environmentally friendly family.