  In situ high pressure XRD diffraction and Raman spectroscopy have been
performed on 12 nm CeO2 nanoparticles. Surprisingly, under quasihydrostatic
condition, 12 nm CeO2 nanoparticles maintain the fluorite-type structure in the
whole pressure range (0-51 GPa) during the experiments, much more stable than
the bulk counterpart (PT=31 GPa). In contrast, they experienced phase
transition at pressure as low as 26 GPa under non-hydrostatic condition
(adopting CsCl as pressure medium). Additionally, 32-36 nm CeO2 nanoparticles
exhibit an onset pressure of phase transition at 35GPa under quasihydrostatic
condition, and this onset pressure is much lower than our result. Further
analysis shows both the experimental condition (i.e., quasihydrostatic or
non-hydrostatic) and grain size effect have a significant impact on the high
pressure behaviors of CeO2 nanomaterials.
