Diffusion behavior of hydrogen isotopes in tungsten revisited by molecular dynamics simulations

Molecular dynamics simulations were performed to study the diffusion behavior of hydrogen isotopes in single-crystal tungsten in the temperature range of 300-2000 K. The simulations show that the diffusion coefficient of H isotopes exhibits non-Arrhenius behavior, though this deviation from Arrhenius behavior is slight. Many-body and anharmonic effects of the potential surface may induce slight isotope-dependence by the activation energy; however, the dependence of the pre-factor of the diffusion coefficient on the isotope mass is diminished. The simulation results for H-atom migration near W surfaces suggest that no trap mutations occur for H atoms diffusing near either W100 or W111 surfaces, in contrast to the findings for He diffusion near W surfaces. Based on the H behavior obtained by our MD simulations, the time evolution of the concentration distribution of interstitial H atoms in a semi-infinite W single crystal irradiated by energetic H projectiles was calculated. The effect of H concentration on H diffusion is discussed, and the applicability of the diffusion coefficients obtained for dilute H in W is assessed.