Synchrotron X-ray diffraction study for crystal structure of solid carbon dioxide CO₂-V

Synchrotron X-ray diffraction study for solid CO₂ at 40–100 GPa and around 2,000 K has shown that the diffraction pattern of the high pressure phase CO₂-V is consistently interpreted in terms of a tetragonal uni_{_}t cell (Z = 4, a = 3.584 Å, c = 5.908 Å at 50GPa). A β-cristobalite structure (space group I2d) gives a good account of our data qualitatively. Isothermal molar volume (300K) of the CO₂-V in the present study is smaller than that indexed as a tridymite structure proposed by previous studies at any pressures.