Tuning Optical\nand Electrical Transport Properties\nin Zero-Dimensional Bismuth-Based Halide Rb<sub>3</sub>Bi<sub>2</sub>I<sub>9</sub> under High Pressure

Bismuth-based perovskite materials\nhave attracted extensive\nattention\ndue to their low toxicity and excellent optoelectronic properties.\nHerein, this investigation delves systematically into the influence\nof pressure on the structural stability, band gap evolution, and electrical\ntransport properties of Rb<sub>3</sub>Bi<sub>2</sub>I<sub>9</sub>.\nWith the pressure increase, the band gap of the specimen gradually\ndiminishes, attaining an optimal semiconductor band gap of 1.34 eV\nat 12.8 GPa, accompanied by obvious piezochromism from red to black.\nA pressure-induced semiconductor-to-metal transition occurs at 15.8\nGPa. Electrons serve as the principal charge carriers in electrical\nconduction, while grain boundary impedance dominates the impedance\nprofile of the sample.