Segregation of Ba2+, Sr2+, Ce4+ and Zr4+ to UO2 surfaces

Segregation of the cation substitution defects Ba2+, Sr2+, Ce4+ and Zr4+ to the stable low index surfaces of UO2 has been predicted using atomistic simulation techniques. While Ce4+ and Zr4+ substitute simply for U4+, charge compensation in the form of oxygen vacancies is required in the case of Ba2+ and Sr2+. Three surfaces are considered: (110), (111) and (100). Although the (111) and (110) are perfect cleaved surfaces, the (100) necessarily incorporates a series of surface defects to neutralize the inherent dipole. The segregation energies of these cations depend strongly on the surface to which the segregation is proceeding. Furthermore, it is also a function of the orientation of the segregating defect cluster with respect to the surface and, in the case of the (100) dipolar surface, the configuration of the surface defects.