Centimeter-Sized Piezoelectric Single Crystal of Chiral Bismuth-Based Hybrid Halide with Superior Electrostrictive Coefficient.

The lead-free hybrid perovskite piezoelectrics possess advantages of easy processing, light weight, and low-toxicity over inorganic ceramics. However, the lack of understanding in structure-property relationships hinders exploration of new molecular piezoelectric crystals with excellent performances. Herein, by introducing chiral α-phenylethylammonium (α-PEA + ) cations into bismuth-based hybrid halides, centimeter-sized (R-α-PEA) 4 Bi 2 I 10 and (S-α-PEA) 4 Bi 2 I 10 single crystals with a superior piezoelectric voltage coefficient g 22 of 309 mV m N -1 , are obtained. Structural rigidity in crystals leads to a remarkable electrostrictive coefficient Q 22 of 25.8 m 4 C -2 , nearly 20 times higher than that of poly(vinylidene fluoride) (PVDF), which is beneficial to improve piezoelectricity with the synergistic effect of chirality. Moreover, the as-grown crystals show outstanding phase stability from 173 K to ≈470 K. This work suggests a design strategy based on rigidity and chirality to exploit novel piezoelectrics among hybrid metal halides.