Phases in ceria-zirconia binary oxide (1-x)CeO2-xZrO2 nanoparticles:: The effect of particle size

The phases of ceria-zirconia nanoparticles observed in air are studied as a function of particle size and composition by X-ray diffraction, transmission electron microscopy, and Raman spectroscopy. The emergence of two tetragonal phases t and t monotonically moves toward higher zirconia concentrations with decreasing particle size. A smaller particle size increases the solubility of zirconia in cubic ceria, while higher zirconia content in ceria stabilizes against coarsening. In particular, the cubic Ce1-xZrxO2-y is persistent and is 8% in phase amount even at 90% zirconia with 33 nm crystal size. Neither the monoclinic phase in nor the tetragonal phase is observed in the present nanoparticles (< 40 nm). The effectiveness of these nanoparticles as oxygen source-and-sink in catalytic support is largely due to the persistence of the cubic and the t phases.