Pressure induced increase of particle size and resulting weakening of elastic stiffness of CeO2 nanocrystals

We demonstrate that the compressibility of cubic fluorite-structure CeO2 nanocrystals s10 nmd increases at pressures above ,20 GPa. At ambient pressure, CeO2 nanocrystals exhibit larger cell parameters than micro-sized samples, and initially exhibit a higher bulk modulus of 328s12d GPa. However, above 20 GPa, the bulk modulus is reduced to 230s10d GPa. Thus, a critical pressure of ,20 GPa was determined that signifies the onset of size-induced weakening of elastic stiffness in nanocrystalline CeO2. Comparison of the x-ray diffraction peaks widths between the platinum standard and CeO2 indicates that a significant increase of particle size in CeO2 appears at a pressure of ,20 GPa. It is suggested that the initial large value of the bulk modulus is a result of either an enhanced surface energy or from the pressure induced stiffness of Young’s modulus sEd and Poisson’s ratio smd; while the weakening of the elastic stiffness above 20 GPa is due to a pressure-induced increase of particle size. © 2004 American Institute of Physics. [DOI: 10.1063/1.1768298]