Synthesis of Edge-Shared Octahedral MAPbBr₃ via Pressure- and Temperature-Induced Multiple-Stage Processes

Abstract

Organic–inorganic halide perovskites possess flexible structures with tunable optical properties at high pressures, but the pressure-induced amorphization limits the understanding and exploration of the structure–property relationships. Herein, we report an edge-shared octahedral MAPbBr3 via multiple-stage transformation of the traditional corner-shared three-dimensional perovskites at high-pressure and high-temperature (P–T) conditions. In situ synchrotron X-ray diffraction reveals that upon heating at 8.7 GPa, the amorphized MAPbBr3 transforms into a high P–T structure above 654 K via multiple-stage crystallization. The high P–T phase is determined to be a monoclinic P2/m structure with layered edge-shared Pb–Br octahedra, which can be quenched to RT at high pressures but converts back to the initial cubic perovskite structure below 0.7 GPa under decompression. The Raman and optical measurements demonstrate that the high P–T phase has similar vibrational behavior and tunable optical properties to those of the pressure-induced amorphous phase, indicating the similarity in the local structure with the edge-shared PbBr6 octahedral frame and the MA organic cations between the high P–T phase and the amorphous state. The present results demonstrate the structural diversity and interconversion in MAPbBr3 by overcoming the large kinetic barrier derived from the anisotropic organic cations and disordering arrangement of the Pb–Br octahedra, providing new insights into the understanding of structural transitions and amorphization of halide perovskites.