Influence of Li on the behavior of H and point defects in vanadium alloys

Abstract

Vanadium alloys are promising structural materials for first wall and blanket applications in advanced fusion reactors. Hydrogen (H) retention strongly affects their stability during operation. Through first-principles calculations and empirical formulas, we investigated the influence of lithium (Li) on the behavior of H and point defects in vanadium alloys. The results showed that Li increases H retention and act as a stabilizing effect on H. The binding of Li-vacancy enhances vacancy-trapping ability for H impurities and the stability of H-vacancy complexes, while Li-vacancy still stably trap six H. Kinetically, H atom migrating to Li exhibits a lower barrier (0.058 eV), in turn it will overcome a high barrier (0.22 eV), indicating Li hindering H mobility. Moreover, the predictions of empirical formulas presented that Li reduces the effective diffusivity of H but increases the permeability of H in vanadium alloy. On the other hand, the Li-vacancy interaction is a weak attraction, kinetically Li decreases migration barrier of vacancy near Li by 0.34 eV, promoting vacancy diffusion in 〈111〉 direction. Li atoms can form Li-vanadium mixed interstitials and reduce the rotation barriers of 〈111〉 _{mixed V-Li}, slowing down self-interstitial diffusion. These findings deep understanding for the synergetic effects of Li with H impurities and point defects in vanadium alloys.