Ab initio study of hydrogen in titanium beryllides

Titanium beryllide Be${}_{12}$Ti is a candidate material for the neutron multiplier for the demonstration fusion reactor DEMO. Experimental studies show that under certain conditions, Be${}_{12}$Ti may contain inclusions of other phases such as Be${}_2$Ti, Be${}_{17}$Ti${}_2$. In this regard, it is extremely important to study the diffusion of tritium and its isotopes in the crystal lattices of these phases. All calculations are performed using ab initio methods. Solution energies of a hydrogen atom in all non-equivalent interstitial sites of the three studied titanium beryllides were found to be lower than that in pure beryllium. The formation energy of all types of vacancies in all studied beryllides is found to be higher than that in beryllium. The binding energies of a single hydrogen atom located both inside and outside the vacancies are calculated. Hydrogen inside monovacancy is more strongly bound as compared to that outside this vacancy. It turned out that in some cases hydrogen can be captured by vacancy being outside of it. The results obtained can be useful for further study of interstitial diffusion of hydrogen and analysis of tritium retention in titanium beryllides.