Exploring the impacts of Li and He impurities in a tungsten matrix: A First-Principles study

Abstract

The liquid Li coating on the plasma-facingmaterials (PFM) has been suggested and implemented as a viable and efficient solution to overcome the damage of plasma on PFM in Tokamak devices. However, the internal mechanisms and impacts of tungsten-based PFM are not yet fully understood. Here, we demonstrate the effects of the impurities with multiple Li atoms, the co-doped Li and He atoms, and the self-trapping induced by the He8/He12 and LiHe8/LiHe12 clusters on the mechanical properties and melting point of W, with the aid of the optimized structures, the formation energies, the charge density distribution, and the density of states obtained by the first-principles calculations. The bulk, shear, and Young moduli, together with the anisotropy factor and Poisson ratio, are calculated for each structure by using the calculated elastic coefficients to understand the effects of impurities on the mechanical properties of W. The results show that the substitutional site in the W matrix is more likely to be occupied by a single Li impurity atom and the impurity He atoms prefer the octahedral interstitial, at the same time, the additional Li impurity atoms are more likely to be located at tetrahedral interstitial sites. The charge density distributions and density of states exhibit that the bond energies involving the highly doped Li or He atoms decrease, which leads to a substantial decrease of elastic coefficients and then obviously reduces the melting points, and the shear and Young moduli, although the impurity of single Li and the self-trapping of the single He8/He12/LiHe8/LiHe12 clusters can maintain these physical quantities as PFM. It implies that the impurity concentration of Li or Li-He in the W matrix should be strictly controlled in the PFM application. Therefore, the present investigations can provide a helpful guide for developing PFM with tungsten.