Structural phase transitions in iodine under high pressure

Abstract

Abstract High-pressure powder X-ray diffraction experiments have been carried out on solid iodine at room temperature. A new intermediate phase V has been identified in the pressure range 24–28 GPa, in the close vicinity of the pressure-induced molecular dissociation. The structure is incommensurately modulated, a rare case for elemental solids. The nearest interatomic distances are distributed over a range 2.8–3.2 Å, which characterizes phase V as a transient state between the molecular and monatomic states. We discuss the overall change of the crystal structure of iodine with pressure, which gives an insight into the process of molecular formation and dissociation.