Influence of carbon–vacancy interaction on carbon and vacancy diffusivity in tungsten

• W and W-alloy are the most promising plasma facing material.
• Defect vacancy can easily trap impurity C atoms to form CnV complexes.
• Synergistic diffusing effect of pure vacancy and CnV complexes in W.
• The effective vacancy diffusion coefficient in W.

We calculate the effective vacancy diffusion coefficient caused by the synergistic migrating effect of pure vacancy and CnV complexes using first-principles calculations combined with statistical model. We demonstrate that at the lower temperature, the CnV complexes can move hardly due to the larger dissolution energy, while with the increasing temperature, these CnV complexes will gradually become mobile. When the temperature increase to T = 1500 K, the effective vacancy diffusion coefficient is equal to that of pure vacancy. When the temperature is further increased and higher than T = 1500 K, all the CnV complexes will dissolve to become isolated vacancies and simultaneously form interstitial C atoms, suggesting that all the CnV complexes do not exist anymore. Finally, by exploring the possible influence of CnV complexes on diffusivity of interstitial C, we find that CnV complexes will almost have no influence on the bulk diffusion of interstitial C through W crystal.