Diffusion and retention of hydrogen in vanadium in presence of Ti and Cr: First-principles investigations

We systemically investigated diffusion and retention of hydrogen (H) in vanadium (V) in presence of Ti/Cr and determined the stability of Hn clusters and Hn-vacancy clusters (n = 1-6) near Cr/Ti using first-principles calculations. H prefers a tetrahedral site near Ti than other interstitial sites. H-Cr interactions have a weak repulsion contrarily H-Ti interactions have a weak attraction. Kinetically, H diffusion barrier decreases towards Ti, while it increases towards Cr. Ti and Cr block H mobility in V alloys. Moreover, Hn Ti clusters are quite stable while HnCr clusters are less stable. Ti enhances H retention by acting as a trapping site for multiple H atoms in similar with vacancy, and a Ti atom can trap at least six H atoms. The stability of H-vacancy-Cr/Ti complexes and vacancy-Cr/Ti trapping for multiple H atoms are discussed. The findings are valuable for understanding the mechanism of H bubble nucleation and H embrittlement under irradiation.