Abstract
This article reviews mainly structural studies on solid halogens, analogous to solid hydrogen, which have been found to undergo successive phase transitions induced by pressure. An extensive x-ray diffraction measurement incorporated with a diamond-anvil cell has revealed both molecular dissociation taking place at 21 GPa and an fcc lattice realized above 55GPa in iodine. These phenomena have been predicted only theoretically in solid hydrogen for a long time. A brief review has also been made on theoretical study of the phase stability and metallic character.
