Effects of niobium on helium behaviors in tungsten：a first-principles investigation

We investigate the effects of niobium (Nb) on helium (He) dissolution and diffusion behaviors in tungsten (W) using a first-principles method. The results show that Nb can effectively reduce the solution energy of He in the bulk W, which is because of the charge density redistribution. This leads to a strong attraction between He and Nb in W, and thus Nb can serve as a He trapping centre in W. The trapping energy of He is 0.37 eV at the most stable site surrounding Nb atom. It is demonstrated that the diffusion barrier of He towards Nb will decrease with the decreasing of He-Nb distance. This suggests that the kinetic process in which He is trapped by Nb is feasible. Therefore, the presence of Nb will facilitate the nucleating and blistering of He in W.