Multiferroic Orders and Piezoelectric Sensing in an Organic‐Inorganic Bismuth Halide

ABSTRACT Multiple ferroic orders integrated into a single material pose great potential for next‐generation sensing, memory and switching devices. Organic‐inorganic hybrid materials (OIHMs) have emerged as promising candidates due to their synergistic combination of functional organic cations and inorganic frameworks. However, obtaining multiferroic materials has long been a continuous challenge, and bismuth‐based OIHM multiferroics remain a blank to date. Here, we report a multiferroic OIHM (DMPA) 3 Bi 2 Br 9 (DMPA = N,N ‐dimethylisopropylamine), which couples ferroelectric and ferroelastic properties for the first time among bismuth‐based OIHMs. Driven by dynamic cation reorientation, (DMPA) 3 Bi 2 Br 9 undergoes multiple symmetry‐breaking processes, enabling m F m ‐type ferroelectric and 3 m F m ‐type multiferroic phase transitions as well as exceptional four‐state SHG transition behaviors. Benefiting from these attributes, (DMPA) 3 Bi 2 Br 9 crystals achieve a notable piezoelectric coefficient d 33 of 35 pC/N, enabling its flexible composite with polyurethane to show excellent piezoelectric sensing responses for pose recognition. This work not only expands the family of multiferroic materials but also underscores their promise for next‐generation flexible electronics and switching devices.