Effect of Ti/Y/O on He Clustering at a Vacancy in Vanadium from First-Principles Calculations

Effect of Ti/Y/O element on helium (He) clustering in vacancy (Vac) defect of vanadium (V) alloy were investigated using first-principles calculations. We first calculated the formation and binding energies of Hen clusters in Vac-X (X = O/O-Ti/O-4Ti/O-3Ti-Y) configurations, the values for O-3Ti-Y configuration are obviously reduced by 0.2-1.6 eV with respect to those of alone Vac. In the presence of O, He still favors the octahedral interstitial site at a Vac. The formation energies of Hen clusters in Vac-O-Ti and Vac-O-4Ti defects are close to those of Vac-O with n = 1-5 (n represents the number of He), which are higher than those of Vac by 3 %. 3Ti-Y considerably increases the formation energies of Hen clusters in Vac-O-3Ti-Y complex over 20 %. The nth He binding energy with Vac-X-Hen_ 1 shows a decreasing fluctuant trend, the attraction of Vac-O-3Ti-Y to He is the smallest among all considered configurations. The presence of Ti-O/Y-Ti-O/O obviously reduce the stability of Vac-He clusters. In addition, we discussed the de-trapping behaviors of He from the Vac-X-Hen complexes and found Hen clusters more easily de-trapped from the Vac-X configuration. The present results show that the formation of Vac-X complex reduces vacancy-trapping ability for more He impurities, leading to lots of small Vac-X-He cluster formation, hindering the formation of larger Hen clusters (He bubbles) in V alloys under irradiation.