Stability of X-C-vacancy complexes (X=H, He) in vanadium from first principles investigations

We investigate interstitial C interactions with H/He, stability of Cn-vacancy/Hn-C-vacancy/Hen-C-vacancy complexes (n = 1-5) and trapping of H/He in C-vacancy/C2-vacancy/H-He-C-vacancy in bcc vanadium using first-principles calculations. Interstitial C-H/C-He interactions are very weak and H/He preferential site keeps unchanged. A vacancy can accumulate two C atoms and the C2-vacancy cluster is more stable than the C-vacancy cluster. The electron localization function analysis shows that the C atoms form strong C-C bonds in vacancy and weaken the C-vanadium bonds. The stable configurations of Hn/Hen-C-vacancy clusters are partially different and the dissolution of H/He from Hn-C-vacancy/Hen-C-vacancy complexes is easier than Hn-vacancy/Hen-vacancy complexes with n ≥ 2. The synergetic interactions of H and He in C-vacancy complex are also investigated and H/He trapping strength decreases in H-He-C-vacancy complex. The presence of C weakens vacancy trapping for more H/He atoms due to large distance of C-H/C-He.