First-Principles Study of the Stability of Ti_nO_m Clusters and He Behavior Inside Ti_nO₂Va₁ Clusters in Vanadium Alloy

In order to characterize the behaviors of interstitial oxygen (O) in the vanadium (V) alloy, the interactions between O and Ti with respect to atomic separation distance have been investigated using first-principles calculations. We observe an attractive interaction between Ti and O within the third nearest neighbor (nn) (3nn) distance. The stability of the Ti-vacancy (Ti-Va) clusters has been studied by calculating the binding energy between Ti and monovacancy in the vanadium alloy, and our results show that the stable configurations are Ti₁Va₁, Ti₂Va₁, and Ti₄Va₁ clusters. The Ti_nVa₁ clusters prefer to trap two O atoms and form stable Ti₁O₂Va₁, Ti₂O₂Va₁, and Ti₄O₂Va₁ clusters. Furthermore, the self-trapping energies of the He_x clusters by the Ti_nO₂Va₁ clusters have been calculated. When four He atoms are trapped, the He_x clusters are stable. Furthermore, the trapping energies for the multiple He atoms captured by the Ti_nO₂Va₁ clusters are calculated, and the Ti_nO₂ clusters are found to impede the vacancy trapping of He atoms to form He bubbles.