THERMAL-STABILITY OF DOPED CERIA - EXPERIMENT AND MODELING

The process of the decrease of the surface area due to crystallite gro wth in ceria at 943 K is described by a kinetic model involving oxygen and cerium diffusion. The experimentally found variations in the rate of crystallite growth are reported as a function of the content (less than or equal to 10% cat.) of dopants, which are the cations Ca2+ Mg2 +, Al3+, Y3+, Sc3+, Al3+, Th4+, Zr4+ and Si4+. The Variations are disc ussed on the basis of the diffusion of cerium vacancies as the rate-li miting step, and on the basis of calculated expressions of the concent rations of oxygen vacancies, electrons and cerium Vacancies vs. the ox ygen partial pressure and the dopant content. For cations that are sma ller than Ce4+, the comparison between the experimental and theoretica l rates asserts the Validity of the model and allows the prediction of the efficiency of a cation to stabilize the surface area, from its as sociations with oxygen vacancies and with the electron-bearing species , Ce-Ce'.