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The effects of high temperature on the high-pressure behavior of CeO2

Raman spectrum and angle-dispersive x-ray diffraction (ADXD) measurements have been performed to investigate the effects of high temperature on the high-pressure behavior of bulk CeO2. A phase transformation of CeO2 from fluorite to PbCl2-type structure occurs at 12.0 GPa and is completed at 14.2 GPa after the sample is heated, and the phase transition pressure decreases by nearly 20 GPa compared with that at room temperature. On decompression, the high-pressure phase of CeO2 remains down to 2.2 GPa, and it changes back to a cubic structure at ambient conditions. At a pressure of 22.1 GPa, a 6.4% lattice volume difference between the fluorite and PbCl2-type structures was observed. The lattice volume of fluorite phase obtained in the areas that have been heated is about 1% less than that obtained in the areas that have not been heated. Besides prompting the phase transition of CeO2, high temperature also anneals the sample and leads a small reduction in lattice volume of the fluorite phase. The zero-pressure bulk modulus of the fluorite phase of CeO2 after annealing is calculated to be about 200 GPa with an assumed pressure derivative of four, which is smaller than that of former x-ray diffraction experiments at room temperature.