First-principles study of intrinsic point defects and Xe impurities in uranium monocarbide
| Autor: | Gui-Yang Huang, Brian D. Wirth, Giovanni Pastore |
|---|---|
| Rok vydání: | 2020 |
| Předmět: |
010302 applied physics
Materials science General Physics and Astronomy 02 engineering and technology Activation energy 021001 nanoscience & nanotechnology 01 natural sciences Molecular physics Crystallographic defect Impurity Lattice (order) Vacancy defect 0103 physical sciences Frenkel defect Density functional theory 0210 nano-technology Phase diagram |
| Zdroj: | Journal of Applied Physics. 128:145102 |
| ISSN: | 1089-7550 0021-8979 |
| DOI: | 10.1063/5.0021951 |
| Popis: | Based on density functional theory (DFT) calculations, we perform an extensive investigation of intrinsic point defects and Xe impurities in uranium monocarbide (UC). The DFT calculations involve both the conventional generalized gradient approximation (GGA) and the GGA+U approach with the Hubbard parametric term (U), using up to 5 × 5 × 5 supercells. GGA calculations for the formation energy of intrinsic defects demonstrate the significant effect of using larger supercells than in previous studies. Results confirm that the ⟨ 111 ⟩ and ⟨ 100 ⟩ dumbbell interstitials are the most stable interstitial configurations for U and C, respectively. The interstitial mechanisms are favored for self-diffusion of both uranium and carbon and diffusion of Xe under equilibrium conditions. Calculations also reveal that the Xe substitutional defect at the C lattice site tends to adopt an off-site configuration, which can be interpreted as a Xe interstitial–C vacancy complex. We also utilize GGA+U to assess the impact of effective U parameter ( U e f f) on the results. Moreover, we introduce a method to estimate the carbon chemical potential by fitting the phase diagram composition data and propose a selection U e f f = 1.25 eV based on the experimental Xe diffusion activation energy. With this approach, GGA+U calculations reproduce the available experimental data for the formation energy of the carbon Frenkel pair and can explain the stepwise recovery of intrinsic properties and burst Xe release behavior in UC observed in annealing experiments. |
| Databáze: | OpenAIRE |
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