Fig. 1.

Pressure-driven structural evolution of MAPbI₃ single crystal. (A) MAPbI₃ single-crystal diffraction pattern at 0.4 GPa at the center detector position. (B and C) Zoomed-in views of MAPbI₃ single-crystal diffraction patterns at 0.4 GPa and 1 atm, respectively. We can see an obvious peak splitting between (330) and (3-30) Bragg reflections at 0.4 GPa in B, demonstrating a symmetry lowering compared with the tetragonal phase at ambient pressure. As expected, no splitting was observed for (220) and (2-20) Bragg peaks at 1 atm in C, consistent with the tetragonal nature. (D) Pb-I inorganic frameworks of MAPbI₃ at 1 atm and 0.4 GPa, from which smaller Pb–I–-Pb bond angles are observed at 0.4 GPa owing to the significantly distorted PbI₆ octahedra.