New Metallic Ordered Phase of Perovskite CsPbI under Pressure.

Pressure-induced electronic structure transition from insulating phase to metal state is a potential new paradigm for halide perovskites. The metallization based on these materials may afford a novel motif toward realizing new electronic properties even superconductivity phenomenon. Herein, how static compression modulates the crystal and electronic structure of typical perovskite semiconductors cesium lead iodine (CsPbI) by both experimental and theoretical studies is reported. The comprehensive studies discover the insulator-metal transition of CsPbI at 39.3 GPa, and reveal the key information behind the electronic transition. The perovskite's precise structural evolution is tracked upon compression, from orthorhombic phase to monoclinic structure before the metallic transition. More interestingly, the phase has the most distorted octahedra and the shortest Pb-I bond length relative to the average bond length that is ever reported in a halide perovskite structure. The electronic transition stems from the structural changes accompanied by the anomalously self-distorted octahedra. These studies show that pressure can significantly alter the structural and electronic properties of these technologically important perovskites.