PRESSURE-INDUCED MONATOMIC TETRAGONAL PHASE OF METALLIC IODINE

An x-ray diffraction study of solid iodine at room temperature has revealed that it undergoes a new phase transition at about 45 GPa from the body-centered-orthorhombic to -tetragonal lattices in its monatomic metallic phase, in addition to the previously-known molecular-to-monatomic transition at 21 GPa. No appreciable discontinuity was observed in the unit cell volume across the transition pressure. This fact leads to an implication of the second order transition. An extrapolation of the present data also implies that a face-centered cubic phase is realized at a much lower pressure than previously predicted.