Tuning Optical and Electrical Transport Properties in Zero-Dimensional Bismuth-Based Halide Rb₃Bi₂I₉ under High Pressure

Bismuth-based perovskite materials have attracted extensive attention due to their low toxicity and excellent optoelectronic properties. Herein, this investigation delves systematically into the influence of pressure on the structural stability, band gap evolution, and electrical transport properties of Rb₃Bi₂I₉. With the pressure increase, the band gap of the specimen gradually diminishes, attaining an optimal semiconductor band gap of 1.34 eV at 12.8 GPa, accompanied by obvious piezochromism from red to black. A pressure-induced semiconductor-to-metal transition occurs at 15.8 GPa. Electrons serve as the principal charge carriers in electrical conduction, while grain boundary impedance dominates the impedance profile of the sample.