Double dependence of H diffusion in tungsten from first-principles determination: strain and temperature

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The hydrogen (H) diffusion in tungsten (W) is an important factor for the use of W as the plasma facing material in a fusion reactor. However, under the environment of fusion, high energy neutron irradiated-W unavoidably leads to the possible local strain so as to cause the lattice expansion or compression, which changes the diffusion behaviors of H in W. In view of this, we have carried out first-principles calculations to determine the interstitial H migration properties under double effects of isotropic strain and temperature in W. For both strain-free and strain-applied (including tension and compression) cases, the H migration energy raises when the temperature rises from 300 to 1800 K. While at each fixed temperature T = 300, ..., 1800 K, the H migration energy can reduce/increase significantly with the increasing tensile/compressive strain. The vibration free energy contribution plays a key role in the H migration energy with the temperature at both strain-free and strain-applied W systems.