Helium diffusion in tungsten: A molecular dynamics study

The diffusion process of He in W is simulated by a molecular dynamics (MD) method with self-developed W-H-He analytic bond-order potentials. The mean squared displacement (MSD) method is employed to determine diffusivity at different temperatures, and then the diffusivity-temperature (D-T) relationship is fitted by the Arrhenius equation to obtain the prefactor and the diffusion barrier. We show the diffusivity of He and the corresponding prefactor and diffusion barrier are different at different temperature ranges. The diffusivities are 9.50 x 10(-9)exp(-0.021 eV/kT) m(2)/s in the temperature range of 50-300 K, 3.61 x 10(-8)exp(-0.057 eV/kT) m(2)/s in 300-1500 K, and 8.562 x 10(-8)exp(-0.157 eV/kT) m(2)/s in 1500-3000 K, respectively, which correspond to different diffusion mechanisms. At a lower temperature, He diffuses directly from one tetrahedral interstitial site (TIS) to another TIS through the diagonal interstitial site with a lower diffusion barrier, while it can diffuse from one TIS to other TIS through the octahedral interstitial site with higher barrier at higher temperature. (C) 2012 Elsevier B.V. All rights reserved.