First principles study of foreign interstitial atom (carbon, nitrogen) interactions with intrinsic defects in tungsten

We performed a series of first-principles calculations to investigate the foreign interstitial atom (FIA) interactions with intrinsic defects in tungsten. We found the following: (i) The introduction of the FIA reduces the vacancy formation energy, resulting in the increase of the equilibrium concentration of vacancies. (ii) The positive binding energy between two FIAs suggests that the FIA can attract other FIAs. (iii) The FIA is easily trapped by the vacancy, and a single vacancy can accommodate up to 4 and 6 atoms in a stable manner for carbon and nitrogen, respectively. (iv) There is an attraction interaction between the FIA and the self-interstitial atom (SIA), and the FIA can reduce the SIA jump frequency and enhance the formation of SIA clusters in tungsten. Moreover, the difference between carbon and nitrogen are also discussed with respect to the formation of FIA–FIA covalent bond and the accumulation around the saturated FIA n – V complex.