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 W{ 100} or W{ 111 } 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.

First-principles investigation of diffusion behaviours of H isotopes:From W(110) surface into bulk and in bulk W

The diffusion behaviours of hydrogen （H）, deuterium （D）, and tritium （T） from W（110） surface into bulk and in bulk W are investigated using first-principles calculations combined with simplified models. The diffusion energy barrier is shown to be 1.87 eV from W（110） surface to the subsurface, along with a much reduced barrier of 0.06 eV for the reverse diffusion process. After H enters into the bulk, its diffusion energy barrier with quantum correction is 0.19 eV. In terms of the diffusion theory presented by Wert and Zener, the diffusion pre-exponential factor of H is calculated to be 1.57×10-7 m2.s-1, and it is quantitatively in agreement with the experimental value of 4.1×10-7 m2.s-1. Subsequently, according to mass dependence （√1/m） of H isotope effect, the diffusion pre-exponential factors of D and T are estimated to be 1.11×10-7 m2.s-1 and 0.91×10-7 m2.s-1, respectively.