Monstoichiomatry and oxygen diffusion in cerium oxide

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Powders of undoped CeOィイD22ィエD2, Nd-doped CeOィイD22ィエD2, etc. were prepared. Crystal growth of these powders under hydrothermal condition was studied and some of them sintered to obtain high density materials. Lattice parameter, density, oxygen diffusion, surface diffusion, etc. of these samples were studied. In the hydrothermal treatment of undoped CeOィイD22ィエD2 and Nd-doped CeOィイD22ィエD2 at 500℃, it was found that the particle size of powder after treatment depends on the concentration of Nd additive. Performing dissolution experiment, it was found that the sample that can be dissolved into water can grew large during the hydrothemal treatment. The lattice parameter of Nd-doped CeOィイD22ィエD2 was found to follow the Vegard's law up to 35% Nd at 500℃.The oxygen diffusion coefficient of high purity CeOィイD22ィエD2 was determined over wide temperature range. Arrhenius plot of the result was divided into two regions. The high temperature region was very close to that or other stoichiometric oxide with fluorite structure and the diffusion in this range was concluded to be in intrinsic region. The slope of low temperature region was very close to those of Y-doped CeOィイD22ィエD2 and Gd-doped CeOィイD22ィエD2 reported in the literature. Plotting oxygen diffusion coefficient in undoped CEOィイD22ィエD2 and doped CEOィイD22ィエD2 as a function of concentration of trivalent cation impurities or additives, the diffusion in this region was found to be controlled by trivalent impurities in the oxide.Surface diffusion in CeOィイD22ィエD2 was determined for the first time. Chemical diffusion in Y-doped CeOィイD22ィエD2 and Y-doped ZrOィイD22ィエD2 was determined. It was slower than oxygen diffusion and close to cation diffusion of Zr in Ca-dopped ZrOィイD22ィエD2.