Energetics of hydrogen and helium-vacancy complexes in bulk and near surfaces of tungsten: First-principles study

• Published in: Journal of applied physics 2018-06, Vol.123 (21)
• Main Authors: Yang, L., Wirth, B. D.
• Format: Article
• Language: English
• Subjects: Applied physics; Binding energy; Charge density; Computer simulation; Density functional theory; Dependence; Divacancies; First principles; Fusion reactors; Helium; Trapping; Tungsten; Vacancies
• ISSN: 0021-8979; 1089-7550
• DOI: 10.1063/1.5027805

Understanding the interaction between hydrogen (H) and helium-vacancy (He-V) complexes in tungsten (W) is important for the development of plasma-facing materials in fusion reactors. H trapping by HexVy complexes in bulk W, as well as the H solution behavior and H trapping by HexV complexes near W(100), W(111), and W(110) surfaces, has been investigated by first-principles computer simulations using density function theory. The results show that the sequential H binding energies to HexV complexes in bulk W decrease with the increasing number of H and He. For the HexV2 complexes in bulk W, H prefers to trap at interstitial sites near the junction of the di-vacancy, where the H can minimize the isosurface of optimal charge density. The most stable interstitial sites for H below W surfaces are dependent on the surface orientation. Our calculations indicate that H atoms tend to prefer a depth of 0.3 nm below the W(100) and W(111) surfaces due to the surface reconstruction. The binding energy of H to a HeV complex near W surfaces has the most significant orientation dependence below the W(111) surface, followed by the W(100) and W(110) surfaces. Compared with the bulk value, the largest difference in the average binding energy of H to the stable HexV complexes at the three W surfaces is about 0.2 eV. Furthermore, the effect of surfaces on the H binding energy to HexV complexes can be ignored for depths greater than 0.65 nm.