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 Ti(1)Va(1), Ti(2)Va(1), and Ti(4)Va(1) clusters. The Ti(n)Va(1) clusters prefer to trap two O atoms and form stable Ti(1)O(2)Va(1), Ti(2)O(2)Va(1), and Ti(4)O(2)Va(1) clusters. Furthermore, the self-trapping energies of the He-x clusters by the Ti(n)O(2)Va(1) 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(n)O(2)Va(1) clusters are calculated, and the TinO2 clusters are found to impede the vacancy trapping of He atoms to form He bubbles.