X-ray Structure Determinations of CeO sub 2 to 70 GPa

X-ray diffraction studies of CeO sub 2 at room temperature on the wiggler polychromatic beam-line at CHESS have confirmed a structural phase transition from the cubic-fluorite structure to an orthorhombic structure at 32 + 2 GPa. The unit cell axial ratios, characteristic diffraction peak extinctions, and relative intensities of the 19 observed powder diffraction peaks at 70 GPa are consistent with the powder diffraction peaks at 70 GPa are consistent with the PbCl sub 2 structure (cotunnite, space group: Pnam) for the high pressure phase.