New High-Pressure Structural Transition of Oxygen at 96 GPa Associated with Metallization in a Molecular Solid

By using a high-energy and high-brilliance synchrotron radiation source in the European Synchrotron Radiation Facility and the Photon Factory, an angle-dispersive powder x-ray diffraction study of solid oxygen has been carried out up to 116 GPa at room temperature. A new high-pressure structural transition was observed at 96 GPa and explained as an isostructural transition with a discontinuous change in lattice constants in a monoclinic cell. Metallization of oxygen reported by Desgreniers, Vohra, and Ruoff [J. Phys. Chem. 94, 1117 (1990)] is ascribed to the transition.