The formation and migration of point defects and the thermodynamic behavior of TiD2 by first-principles calculations

TiD2 has important applications in nuclear materials, for example neutron generator. Therefore, it is of great importance to study the evolution of the defects in TiD2 during the service. In this work, first-principles calcu-lations are performed to study the formation and migration behaviors of point defects in TiD2, as well as the phase stability of TiD2. The formation energies of Ti vacancy (VTi) and D vacancy (VD) in TiD2 are 2.34 and 0.73 eV, respectively. The migration barriers of VD are 0.80 and 0.66 eV for the migration path within ab plane and bc plane, respectively, which is much lower than the those of the interstitial D atoms. So, the predominant diffusion mechanism of a D atom in TiD2 is the vacancy hopping mechanism. Furthermore, we find that VTi will trap interstitial D atoms and D vacancies. At last, the thermal stability of TiD2 is investigated and we find that interstitial D atoms and D vacancies are formed during the molecular dynamics simulations at 1200 K. This work presents a microscopic picture for the formation and transformation of the point defects in TiD2.