Vacancy and H Interactions in Nb

The vacancy and H interactions in bcc Nb are important due to their implication in understanding of the H induced damage of Nb metallic membrane used in H2 separation and purification application. Using density functional theory, the vacancy formation energy and vacancy (Vac)-H interaction energies are calculated. The results show that vacancies have a strong trapping effect on H atoms, which lowers the formation energy of Vac-nH clusters substantially. The concentration of Vac-nH clusters is evaluated using a statistical model and the dependence of the concentration on the H-to-M ratio is obtained. It is shown that the concentration of the Vac-nH clusters can be as high as 10−3 at 573K, i.e. one Vac-nH cluster per 1000 atoms, in good agreement with the experimental observations. (condensed matter: electronic structure, electrical, magnetic, and optical properties)