High-pressure Raman study of CeO<SUB>2</SUB> to 35 GPa and pressure-induced phase transformation from the fluorite structure

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 (F2g) and the shifts of several second-order features were measured. The Gruneisen parameter for the F2g mode (465 cm-1) is obtained as &#947;=1.44 and for the F1u (&#969;LO=585 cm-1) as &#947;=1.5; the latter from the 2&#969;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