A high pressure Raman study of Ce0 sub 2 to 35 GPa and pressure- induced phase transformation from the fluorite structure.

Cerium dioxide (Ce0 sub 2) which crystallizes in the fluorite structure has been studied by high pressure Raman spectroscopy using a diamond anvil cell, up to 35 GPa. The pressure shift of the first-order fluorite Raman peak (F sub (2g)) and the shifts of several second-order features were measured. The Gruneisen parameter for the F sub (2g) mode (465 cm sup (- 1)) is obtained as gamma=1.44 and for the F sub (1u)(omega sub (LO) = 585 cm sup (-1)) as gamma = 1.5; the latter from the 2omega sub (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 PbCl sub 2-type structure. The high pressure phase is found to be metastable over 20 GPa interval, but completely reverses on releasing pressure.