The pressure dependence of the first-order Raman peak and two second-order Raman features of ThO2 crystallizing in the fluorite-type structure is investigated using a diamond anvil cell, up to 40GPa. A phase transition from the fluorite phase is observed near 30 GPa as evidenced by the appearance of seven new Raman peaks. The high pressure phases of ThO2 and CeO2 exhibit similar Raman features and from this it is believed that the two structures are the same, and have the PbCl2-type structure. The pressure dependence dω/dP of the observed phonons and their mode Grüneisen parameters are similar to the isostructural CeO2. The observed second-order Raman features are also identified from the calculated phonon dispersion curves for ThO2.
Volume 94, 2020
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