Journal
NUCLEAR INSTRUMENTS & METHODS IN PHYSICS RESEARCH SECTION B-BEAM INTERACTIONS WITH MATERIALS AND ATOMS
Volume 266, Issue 12-13, Pages 2671-2675Publisher
ELSEVIER
DOI: 10.1016/j.nimb.2008.03.226
Keywords
uranium mononitride (UN); Frenkel defects; O impurity; defect migration; first-principles calculations; supercell model
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We present and discuss the results of the first-principles calculations of Frenkel defects and O impurities in uranium mononitride (UN) perspective for fast reactor nuclear fuels. Special attention is paid to the calculation of defect migration energies. We demonstrate that the interstitialcy mechanism (with the formation of a N-N dumbbell along the [111] axis) is energetically more favorable than the direct [100] hops. As a result, for the interstitial N ions we predict a diffusion mechanism similar to that known in isostructural fcc materials with a different chemical nature (KCl, MgO). The calculated effective N charge considerably depends on the ion position and environment (a host lattice site, interstitial or saddle point) which strongly limits the applicability of classical defect modelling based on formal invariant charges. Lastly, the calculated migration energy for the interstitial impurity O ions is quite low (2.84 eV), which indicates their high mobility and ability for reactions with other defects. (c) 2008 Elsevier B.V. All rights reserved.
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