Structural Characterization of Ceria-Zirconia Powder Catalysts Prepared by High-Energy mechanical Milling: A Neutron Diffraction Study

Neutron diffraction measurements were carried out on samples of CeO2-ZrO2 powder catalysts prepared by high-energy mechanical milling. The formation of solid solution was evidenced across the entire composition range examined. Quantitative phase evaluation by the Rietveld method indicated formation of tetragonal structure for low CeO2 content, whereas cubic solid solutions were the stable form at high CeO2 loading, In addition, a pseudocubic or tetragonal t " cell with axial ratio of unity and with internal deformation of the oxygen sublattice was observed at intermediate composition (50 mol% CeO2). Thermal annealing up to 1000 degrees C showed expansion of the unit cell parameters; an increase in the degree of tetragonality at the expense of cubic and monoclinic phase was observed for composition CexZr1-xO2 (x < 0.5).