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 573 K, i.e. one Vac-nH cluster per 1000 atoms, in good agreement with the experimental observations.