Structures and transitions in solid O2 to 13 GPa at 298 K by x-ray diffraction

The structures and phase transitions in solid O2 were studied at 298 K from 6 to 13 GPa using powder x-ray diffraction in an anvil cell. Pressures were determined from the compression of in situ NaF. X-ray photographs at various pressures showed patterns from five different phases of O2, two of which were previously unreported. Values of the bulk modulus and volume were derived up to 11 GPa where transition to epsilon-O2 occurs. A compromise fit to all available data indicates that epsilon-O2 may be an orthorhombic distortion of delta-O2