The stability and diffusion properties of foreign impurity atoms on the surface and in the bulk of vanadium: A first-principles study

Vanadium-based alloy is an attractive candidate for the first-wall or blanket structural materials in future fusion reactors. Foreign impurity atoms (FIAs), such as C, O and N, will seriously affect the mechanical and chemical properties of vanadium-based alloy. With first-principles DFT calculations and CI-NEB method, the stability and diffusion properties of FIAs on the surface and subsurface and in the bulk of metallic vanadium have been studied in details. It is found that the most preferred sites are the hollow ones for the FIAs on V(1 0 0) surface. C and N atoms prefer the TIS2–OIS2 site but O atom favors the TIS1-bridge site in the subsurface. O atom is easier to diffuse on the (1 0 0) surface. C atom has the highest barrier from the surface to the subsurface, but can diffuse easily from TIS1 to TIS2 in the subsurface. C, O and N atoms all prefer the OIS in the bulk. The diffusion barrier of N atom in vanadium bulk is the highest, while the diffusion coefficient of C atom is the largest. Electronic properties of FIAs on the surface and in the bulk have also been discussed and it is found that the FIAs at the preferred sites gain more electrons than those at the other sites.