Characterization of the energetics and configurations of hydrogen in vacancy clusters in tungsten. (4th September 2019)

• Record Type: Journal Article
• Authors: Ren, Qing-Yuan; Li, Yu-Hao; Zhou, Hong-Bo; Li, Zhong-Zhu; Cheng, L.; Lu, Guang-Hong
• Is Part Of: Nuclear fusion. Volume 59:Number 10(2019:Oct.)
• Publication Date: 2019-09-04
• Subjects: tungsten -- hydrogen -- vacancy clusters -- energetics and configurations -- trapping and retention; Nuclear fusion -- Periodicals; 621.48405
• DOI: 10.1088/1741-4326/ab36a4
• Languages: English
• ISSNs: 0029-5515

Abstract

Abstract: We have explored the retention of hydrogen (H) in tungsten (W) by investigating its dissolution and aggregation in vacancy clusters (VCs) using a first-principles method and thermodynamic models. The solution energy of a single H in the VCs is in the range of −0.99 to −0.64 eV, much lower than that at a mono-vacancy (~ −0.37 eV) and interstitial site (~1.01 eV) in W. Such a remarkable discrepancy is rationalized on the electronic interaction of H with its neighboring W atoms, which varies from repulsion to attraction with H moving from perfect crystal to vacancy/VCs. Specifically, the solution/trapping energies of H in VCs can be well categorized by the coordination number of its neighboring W atoms, i.e. the lower the coordination number of W, the stronger the H–W attraction and the lower the H solution/trapping energy. Furthermore, taking the cluster as an example, it is observed that the multiple H atoms form a multilayer nested cage configuration at the VC surface initially, and then the stable H2 molecules form in the center of the VCs. Interestingly, the pre-existing H atoms in the VC inner surface have a shielding effect on the H–W interaction, decreasing the electron density of the central region of the VCs and facilitating the formation of H2 molecules. Moreover, the desorption temperatures of H in the VCs are also predicted based on the Polanyi–Wigner equation, and are in good agreement with the available thermal desorption spectroscopy experiments. Our calculations provide a good reference to understand the influence of VCs on the retention and evolution of H in W.