Pressure-induced face-centered-cubic phase of monatomic metallic iodine

Abstract

An x-ray diffraction study of solid iodine at room temperature has revealed that it undergoes a new phase transition at 55\ifmmode\pm\else\textpm\fi{}2 GPa from the face-centered-tetragonal to -cubic phases in its monatomic metallic state. This is the first observation of the fcc Bravais lattice realized in diatomic molecular crystals. Such an isotropic fcc structure is ultimately accomplished after three successive transitions, two of which are the molecular dissociation at 21 GPa and the orthorhombic-to-tetragonal transition at 43 GPa previously observed.