First-principles investigation on 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 a 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 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.