High-pressure Raman study ofCeO2to 35 GPa and pressure-induced phase transformation from the fluorite structure

Abstract

Cerium dioxide (${\mathrm{CeO}}_2$), which crystallizes in the fluorite structure, has been studied by high-pressure Raman spectroscopy with use of a diamond anvil cell, up to 35 GPa. The pressure shift of the first-order fluorite Raman peak ($F_{2g}$) and the shifts of several second-order features were measured. The Grüneisen parameter for the $F_{2g}$ mode (465 ${\mathrm{cm}}^{\mathrm{-}1}$) is obtained as γ=1.44 and for the $F_{1u}$ (${\omega }_{\mathrm{LO}=585\mathrm{}}$ ${\mathrm{cm}}^{\mathrm{-}1}$) as γ=1.5; the latter from the 2${\omega }_{\mathrm{LO}}$ shift in the second-order spectrum. Near 31 GPa, a phase transition occurs and six new Raman peaks appear. By comparison with the high-pressure phases of alkaline-earth difluorides, the high-pressure phase is believed to be of the ${\mathrm{PbCl}}_2$-type structure. The high-pressure phase is found to be metastable over a 20-GPa interval, but completely reverses on releasing pressure.