ROLE OF DEFECT INTERACTION IN BOUNDARY MOBILITY AND CATION DIFFUSIVITY OF CEO2

Grain boundary mobility of CeO2 containing 0.1% and 1.0% trivalent dopant cations (Sc, Yb, Y, Gd, and La, in order of increasing ionic radius) has been measured. At the lower dopant concentration (intrinsic regime), mobility is controlled by grain boundary diffusion of host cations, whereas at the higher dopant concentration (extrinsic regime), mobility is controlled by solute drag through the lattice. The effect of trivalent dopants is closely associated with their ability to provide and to interact with oxygen vacancies. Evidence consistent with an interstitial mechanism for cation diffusion has been found which is remarkably affected by the presence of oxygen vacancies. Ce diffusion is enhanced by free oxygen vacancies in the system, while dopant diffusion is suppressed if a dopant-associated oxygen vacancy is not present. A bare Sc cation, however, appears to be a fast-diffusing species, due to its highly distorted local environment, while Y at 1.0% emerges as the most effective grain growth suppressant.