Impact of Homogeneous Strain On Uranium Vacancy Diffusion In Uranium Dioxide

Authors

Anuj Goyal, University of Florida
Simon R. Phillpot, University of Florida
Gopinath Subramanian, University of Southern MississippiFollow
David A. Andersson, Los Alamos National Laboratory Materials Science and Technology Division
Chris R. Stanek, Los Alamos National Laboratory Materials Science and Technology Division
Blas P. Uberuaga, Los Alamos National Laboratory Materials Science and Technology Division

Document Type

Article

Publication Date

3-3-2015

Department

Physics and Astronomy

School

Mathematics and Natural Sciences

Abstract

We present a detailed mechanism of, and the effect of homogeneous strains on, the migration of uranium vacancies in UO₂. Vacancy migration pathways and barriers are identified using density functional theory and the effect of uniform strain fields are accounted for using the dipole tensor approach. We report complex migration pathways and noncubic symmetry associated with the uranium vacancy in UO₂ and show that these complexities need to be carefully accounted for to predict the correct diffusion behavior of uranium vacancies. We show that under homogeneous strain fields, only the dipole tensor of the saddle with respect to the minimum is required to correctly predict the change in the energy barrier between the strained and the unstrained case. Diffusivities are computed using kinetic Monte Carlo simulations for both neutral and fully charged state of uranium single and divacancies. We calculate the effect of strain on migration barriers in the temperature range 800–1800 K for both vacancy types. Homogeneous strains as small as 2% have a considerable effect on diffusivity of both single and divacancies of uranium, with the effect of strain being more pronounced for single vacancies than divacancies. In contrast, the response of a given defect to strain is less sensitive to changes in the charge state of the defect. Further, strain leads to anisotropies in the mobility of the vacancy and the degree of anisotropy is very sensitive to the nature of the applied strain field for strain of equal magnitude. Our results suggest that the influence of strain on vacancy diffusivity will be significantly greater when single vacancies dominate the defect structure, such as sintering, while the effects will be much less substantial under irradiation conditions where divacancies dominate.

Comments

© Physical Review B. Published version found at 10.1103/PhysRevB.91.094103.

Publication Title

Physical Review B - Condensed Matter and Materials Physics

Volume

91

Issue

9

Recommended Citation

Goyal, A., Phillpot, S., Subramanian, G., Andersson, D., Stanek, C., Uberuaga, B. (2015). Impact of Homogeneous Strain On Uranium Vacancy Diffusion In Uranium Dioxide. Physical Review B - Condensed Matter and Materials Physics, 91(9).
Available at: https://aquila.usm.edu/fac_pubs/18698