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.