High-pressure x-ray diffraction study ofCeO2to 70 GPa and pressure-induced phase transformation from the fluorite structure

The crystal structure of ${\mathrm{CeO}}_2$ has been investigated to 70 GPa using energy dispersive x-ray diffraction in a diamond-anvil cell. At 31.5±1.0 GPa the fluorite phase transforms, on loading, to an orthorhombic α-${\mathrm{PbCl}}_2$-like structure of space group Pnam, with a 7.5%±0.7% increase in density. The cubic fluorite phase has a bulk modulus $B_0$=230±10 GPa with an assumed pressure derivative of $B_0^{\mathcal{’}}$=4.00. The α-${\mathrm{PbCl}}_2$-type structure seems to be the stable high-pressure phase in the case of the group-IVB, lanthanide, and actinide fluorite-type dioxides, independent of metal-ion size, at reduced volumes less than 0.89±0.01.