Point defects in uranium dioxide: Ab initio pseudopotential approach in the generalized gradient approximation

Freyss, Michel; Petit, T.; Crocombette, Jean-Paul

doi:10.1016/j.jnucmat.2005.07.003

Cited by 127 publications

(121 citation statements)

References 20 publications

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“…Table 1 shows a selected list of values calculated by various density functional theory approximations or DFTs (except [46], which uses the Mott-Littleton approximation). From this table, we see that the GGA result in [47] agrees well with the best estimate value recommended by Matzke, whereas the LDA + U result of Andersson et al [50] conforms with the aforementioned experimentally determined result taken from [54,20]. Nevertheless, for H F , there is a range of values, from 3.6 to 4.9 eV, resulting from various computations.…”

Section: Frenkel Defect Formation Energysupporting

confidence: 83%

Effect of additives on self-diffusion and creep of UO 2

Massih

Jernvist

2015

Computational Materials Science

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The creep of UO 2 doped with Nb 2 O 5 and Cr 2 O 3 has been assessed using a point defect model based on the law of mass action, and the diffusional creep according to the Nabarro-Herring mechanism, which relates the creep rate to the lattice self-diffusivity, the inverse of grain area and the applied stress. The self-diffusion coefficients of cation (U) and anion (O) are directly proportional to the concentrations of ions, which in turn are functions of dopant concentrations. The model has been used to evaluate past creep experiments on UO 2 doped with Nb 2 O 5 and Cr 2 O 3 in concentrations up to about 1 mol.%, with a varying grain size at different temperatures and applied stresses. The creep rate increases significantly with the dopant concentration and the putative model, after a modification of the creep rate coefficient, retrodict the measured data satisfactorily. A number of factors affecting creep rate and thereby our model computations are discussed.

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Section: Frenkel Defect Formation Energysupporting

confidence: 83%

Effect of additives on self-diffusion and creep of UO 2

Massih

Jernvist

2015

Computational Materials Science

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“…[62][63][64][65] However, a detailed exploration of the defect energies, energy barriers and uranium migration paths has only been made possible recently by first-principles based density functional theory (DFT) calculations. [20][21][22][66][67][68] In this study, we use the work of Andersson et al 21 in which various charged single uranium vacancies and their clusters have been studied for UO 2−x , UO 2 and UO 2+x , both for intrinsic and irradiation conditions. For stoichiometric UO 2 , the fully charged uranium vacancy (V U ) is the thermodynamically stable defect 20,66,69 and hence control uranium diffusion.…”

Section: A Migration Paths and Energy Barriersmentioning

confidence: 99%

Impact of homogeneous strain on uranium vacancy diffusion in uranium dioxide

et al. 2015

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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 (DFT) and the effect of uniform strain fields are accounted for using the dipole tensor approach. We report complex migration pathways and non-cubic 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 (KMC) simulations for both neutral and fully charged state of uranium single and di-vacancies. 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 di-vacancies of uranium, with the effect of strain being more pronounced for single vacancies than di-vacancies. 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 di-vacancies dominate.

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“…[2][3][4][5] They investigated the electronic structure of the defect systems, and estimated the formation energies of several types of point defects in UO 2 . Their results qualitatively provided the correct trend of defect formation in UO 2 .…”

Section: Introductionmentioning

confidence: 99%

“…UO 2 is well known to be a conventional Mott insulator, 6) but in the framework of the LDA or GGA, UO 2 is predicted to be a metal. [2][3][4][5] This failure of the conventional LDA or GGA has been attributed to the absence of strong correlations for the 5f electrons in the uranium atom in UO 2 . The LDA+U 7,8) method has been developed to describe such a correlation by introducing a strong intra-atomic interaction.…”

Section: Introductionmentioning

confidence: 99%

First-Principles Calculation of Point Defects in Uranium Dioxide

et al. 2006

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A first-principles calculation for uranium dioxide (UO 2 ) in an antiferromagnetic structure with four types of point defects, uranium vacancy, oxygen vacancy, uranium interstitial, and oxygen interstitial, has been performed by the projector-augmented-wave method with generalized gradient approximation combined with the Hubbard U correction. Defect formation energies are estimated under lattice relaxation for supercells containing 1, 2, and 8 unit cells of UO 2 . The electronic structure, the atomic displacement and the stability of defected systems are obtained, and the effects of cell sizes on these properties are discussed. The results form a self-consistent dataset of formation energies and atomic distance variations of various point defects in UO 2 with relatively high precision. We show that a supercell with 8 UO 2 unit cells or larger is necessary to investigate the defect behavior with reliable precision, since point defects have a wide-ranging effect, not only on the first nearest neighbor atoms of the defect, but on the second neighbors and on more distant atoms.

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Point defects in uranium dioxide: Ab initio pseudopotential approach in the generalized gradient approximation

Cited by 127 publications

References 20 publications

Effect of additives on self-diffusion and creep of UO 2

Effect of additives on self-diffusion and creep of UO 2

Impact of homogeneous strain on uranium vacancy diffusion in uranium dioxide

First-Principles Calculation of Point Defects in Uranium Dioxide

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