Atomic force microscopy study of surface diffusion in polycrystalline CeO2 via grain boundary grooving

Abstract

CeO2 powder prepared by isothermally aging cerium (III) nitrate solution at 303 K in the presence of hexamethylenetetramine was sintered at 1723 K for 2 h. This process yielded polycrystalline CeO2 having a relative density equal to approximately 97.6% of its theoretical density. Polycrystalline CeO2, finely polished and examined by atomic force microscopy (AFM), was used to develop thermal grain boundary grooves at different temperatures (1473-1663 K) and times (t=30-480 min) in air. Subsequently, AFM was used to observe the surface morphological change in the annealed polycrystalline CeO2 in order to measure the width, W, and the dihedral angle ψ of the developed grain boundary grooves. AFM observation revealed logW-log t relationships that are approximately linear with slopes of approximately 1/4. An analysis according to Mullins' formulas showed that grain boundary grooving is controlled by surface diffusion. Finally, the surface diffusion coefficient of polycrystalline CeO2 was calculated at different temperatures (1473-1663 K), and the obtained diffusion coefficient was considered to correspond to that of a (CeO2)n group transportation.