Centimeter-sized single crystal of a lead-free halide double perovskite with ferroelastic phase transition-triggered switchable dielectric properties

Driven by the breakthrough development of lead (Pb)-based halide perovskites, halide double perovskites have also emerged as remarkably multipurpose materials owing to their environmental friendliness, abundant physicochemical properties, and structural tunability. However, despite their recent soaring progress, the realization of switchable dielectrics in this fascinating family remains considerably less explored. In this study, centimeter-sized single crystals of a single-layer halide double perovskite (3-bromopropylaminium)(4)AgBiBr8 (1) with dimensions up to 20 mm x 17 mm x 5 mm have been successfully synthesized by using the solution cooling method. The single crystal undergoes a ferroelastic phase transition of mmmF2/m defined by the Aizu notation, which is attributed to the synergistic interaction between octahedral distortion and flexible molecular motion according to structural analysis. Noteworthily, it possesses desirable ferroelastic phase transition-triggered switchable dielectric properties near the high temperature of 373 K, which can be switched between two stable dielectric states. Additionally, 1 possesses an indirect-bandgap semiconducting feature and exhibits an X-ray response with a sensitivity of up to 517 mu C Gy(air)(-1) cm(-2) at a 40 V bias voltage. We believe that this study provides another efficient application path for Pb-free halide double perovskites with intelligent functions.