Mechanisms of the defect formation and diffusion of cations on the surface of uranium dioxide nanocrystals: Molecular dynamics study

Mass transfer and cation diffusion mechanisms on the surface of UO2 nanocrystal were investigated by the high-speed MD method using GPU. Stoichiometric uranium dioxide nanocrystals of 12,000 ions were simulated with two interaction potentials sets. Three regions on the nanocrystal surface with significantly different activation energies were separated. It is shown that the overall mass transfer on the surface is limited by the diffusion of cations on edges connecting (1 0 0) facets. The calculated diffusion activation energy of 5.2 eV is close to the experimental one of 4.7 eV. Estimations of the thickness of the diffusion surface layer were carried out. It is shown that the diffusion of cations in the bulk is fully associated with the migration of Schottky cation vacancies, which are formed on (1 0 0) surfaces. The calculated formation energy of a Schottky trio of 6.6 eV is close to the experimental estimation of 6.5 eV, but significantly differs from the value of 9.8 eV, derived by the standard lattice statics method. (C) 2015 Elsevier B.V. All rights reserved.