Role of di-interstitial clusters in oxygen transport in UO_2+x from first principles

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D. A. Andersson,¹ T. Watanabe,² C. Deo,³ and B. P. Uberuaga¹
¹Materials Science and Technology Division, Los Alamos National Laboratory, Los Alamos, New Mexico 87545, USA
²School of Chemical and Biomolecular Engineering, Georgia Institute of Technology, Atlanta, Georgia 30332, USA
³Nuclear and Radiological Engineering Program, George W. Woodruff School of Mechanical Engineering, Georgia Institute of Technology, Atlanta, Georgia 30332, USA

Received 1 July 2009; published 10 August 2009

Usingdensity functional theory, we examine a recently discovered structure fordi-interstitial oxygen clusters in UO_2+x in which three oxygen ionsshare one lattice site. This di-interstitial cluster exhibits a fastdiffusion pathway; the migration barrier for these clusters is approximatelyhalf of that for mono-interstitials. Using kinetic Monte Carlo, wecalculate the diffusivity of oxygen with and without the di-interstitialmechanism as a function of x and find that oxygentransport is significantly increased for higher values of x whenthe di-interstitial mechanism is included, agreeing much more closely withexperimental data. These results emphasize the importance of clustering phenomenain UO_2+x and have implications for the evolution of UO_2+x.

URL:	http://link.aps.org/doi/10.1103/PhysRevB.80.060101
DOI:	10.1103/PhysRevB.80.060101
PACS:	61.72.Bb; 66.30.Dn; 66.30.H- 61.72.Bb Theories and models of crystal defects 66.30.Dn Theory of diffusion and ionic conduction in solids 66.30.H- Self-diffusion and ionic conduction in solid nonmetals YEAR: 2009
KEYWORDS:	density functional theory, diffusion, interstitials, Monte Carlo methods, uranium compounds

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