In the present study, the phase transitions of bromine have been investigated using high-pressure x-ray diffraction experiments and ab initio calculations up to 230 and 180 GPa, respectively. At pressures beyond molecular dissociation, $Immm, I4/mmm$, and $Fm\overline{3}m$ phases are found, in agreement with the structural sequence found for iodine. We find that the phase transitions are remarkably sluggish—most notably for the $Immm\text{−}I4/mmm$ transition where the two phases coexist from 105(7) to 163(10) GPa, and the transition is observed to result in a small volume discontinuity. By symmetry, these phases are directly related, and ab initio calculations show no energetic barrier between them. However, calculations of the static enthalpy landscape of the close-packed phases under pressure reveal a highly anharmonic potential energy surface, resulting in strong entropic effects when investigating the phase transitions of dissociated bromine.

Close

PrevNext

View figure in article

• High-pressure studies
• Structural phase transition
• Density functional calculations
• X-ray powder diffraction