High-Pressure Studies on CeO 2 Nano-Octahedrons with a (111)-Terminated Surface

In-situ high-pressure X-ray diffraction and Raman spectroscopies have been performed on well-shaped CeO 2 nano-octahedrons enclosed by eight (111) planes. The CeO 2 nano-octahedrons are shown to be more stable than their bulk counterparts and some other reported CeO 2 nanocrystals of smaller size. The transition pressure from cubic to orthorhombic phase is approximately 10 GPa higher than that of 12 nm CeO 2 nanocrystals even though they have similar volume expansion at ambient conditions. Additionally, the phase transition to α-PbCl 2 phase is very sluggish and uncompleted even up to 55 GPa. The TEM image of the sample after decompression from 55 GPa clearly shows that the nano-octahedrons preserve the starting shape. Such distinct high-pressure behaviors in CeO 2 nano-octahedrons have been discussed in terms of their special exposure surface. Further analysis shows that the lower compressibility of the exposed (111) planes in the nano-octahedrons is believed to be the major factor to the elevation of the phase transition pressure and the sluggishness of the transition.