In situ x-ray diffraction study of the pressure-induced phase transformation in nanocrystalline CeO2 - art. no. 012102

The x-ray-diffraction study of nanosized CeO2 was carried to pressures of 3 8.6 Cpa using an energy dispersive synchrotron-radiation technique in a dia mond-anvil cell. At a pressure of 22.3 Cpa, nano-CeO2 starts to transform t o an orthorhombic alpha -PbCl2 structure. This pressure is significantly lo wer than the transition pressure of 31 Cpa for phase transformation in the bulk CeO2. The high-pressure phase is unquenchable and distorts to a hexago nal structure upon release of pressure to ambient conditions. The nanosized cubic fluorite phase has a bulk modulus (B-0) of 328 +/- 12 GPa, much high er than that of the macrosize CeO2 with a B-0 of 230 Cpa. There is a large volume decrease of 9.4% in phase transformation from the fluorite to alpha -PbCl2 structure. Such a phase transformation may occur via a large volume collapse and an unstable high-pressure phase causing a reduction of transit ion pressure in this type of nanomaterial.