High-pressure Raman study of CeO₂ to 35 GPa and pressure-induced phase transformation from the fluorite structure

Abstract

Cerium dioxide (CeO₂), 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 Gruneisen parameter for the F_2g mode (465 cm^-1) is obtained as γ=1.44 and for the F_1u (ω_LO=585 cm^-1) as γ=1.5; the latter from the 2ω_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 PbCl₂-type structure. The high-pressure phase is found to be metastable over a 20-GPa interval, but completely reverses on releasing pressure.