Reexploration of Structural Changes in Element Bromine through Pressure-Induced Decomposition of Solid HBr

Simple molecular solids have been an important subject in condensed matter physics, particularly for research of pressure-induced molecular dissociation. We re-explore the structural changes of element bromine through pressure-induced decomposition of solid HBr. The phase changes in HBr are investigated by Raman spectroscopy and synchrotron x-ray diffraction up to 125 GPa at room temperature. By applying pressure, HBr decomposes into solid bromine in the pressure range of 18.7–38 GPa. The solid bromine changes from molecular phase to incommensurate phase at 81 GPa, and finally to monatomic phase at 91 GPa. During the process of pressure-induced molecular dissociation, the intermediate incommensurate phase of element bromine is confirmed for the first time from the x-ray diffraction studies. The decomposition of HBr is irreversible since HBr cannot form again upon pressure decompression.