First-principles study of the behavior of O, N and C impurities in vanadium solids

Vanadium alloys are promising candidate for the structural materials of first-wall in future fusion reactor. In realistic vanadium alloys, there always exist some impurities (e.g. oxygen, nitrogen and carbon). To understand the microscopic behavior of these impurities, we investigated energetic and diffusion of O, N and C impurities as well as O–O/N–N/C–C interactions in pure vanadium using first-principles calculations. The O, N and C atoms prefer to occupy an octahedral interstitial site, and exhibit high diffusion barrier with 1.23 eV, 1.48 eV and 1.14 eV via diffusing between two neighboring octahedral interstitial sites, respectively. Such high barriers indicate that these impurities are hard to diffuse inside bulk vanadium. The corresponding diffusion coefficients as function of temperature were estimated using the Arrhenius diffusion equation. Our theoretical results provide the fundamental parameters for understanding the impurity effects in early stage of irradiation damage.