Anomalous quasihydrostaticity and enhanced structural stability of 3 nm nanoceria

High-pressure ruby fluorescence spectroscopy and synchrotron X-ray diffraction are used to investigate the differential stress development and structural stability of 3 nm ceria. Upon compression of nanoceria to similar to 28.2 GPa, R-1 and R-2 lines of ruby remain consistent in shape and sharpness. X-ray diffraction displays no reasonable evidence of peak broadening to 28.6 GPa and phase transformation to 65.1 GPa. These observations suggest an anomalous quasihydrostatic state of compressed nanoceria and a highly enhanced structural stability. Although a pressure-driven oxygen release and subsequent vacancy-induced interface superfluid reasonably explains the generation of extended quasihydrostaticity, a particle size dependent isotropic stress field and surface energy contribution to total energy explain a reversal of structural stability as compared to the size-induced reduction of transformation pressure in large scale nanoceria. These findings provide significant information not only for understanding the reversed Hall-Petch relation of nanomaterials but also for synthesizing engineering materials with tunable mechanical properties.