High-pressure x-ray diffraction study of CeO₂ to 70 GPa and pressure-induced phase transformation from the fluorite structure

Abstract

The crystal structure of CeO₂ 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-PbCl₂-like structure of space group Pnam, with a 7.5%±0.7% increase in density. The cubic fluorite phase has a bulk modulus B₀=230±10 GPa with an assumed pressure derivative of B₀'=4.00. The α-PbCl₂-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.