Study of hydrogen diffusion in Nb–Ta alloys by Gorsky effect measurement

Hydrogen diffusion in NbxTa1−x alloys (x = 0, 0.1, 0.25, 0.5, 0.75, 0.9 and 1.0) was investigated over a temperature range between 160 and 340 K by measurements of the Gorsky effect. The temperature dependence of the hydrogen diffusivity, D, of specimens with x = 0, 0.9 and 1.0 showed a deviation from the Arrhenius type behavior at low temperatures, while the other alloys did not show such a deviation. The value of D   decreases with alloying at both the Nb- and Ta-rich ends and exhibits a minimum at x≃0.50x≃0.50. The concentration dependence of D is stronger at the Nb-rich end than that at the Ta-rich end. The hydrogen potential obtained by a first-principles calculation shows that a Ta atom acts as a trapping center for hydrogen in the Nb matrix and a Nb atom acts as an anti-trapping center in the Ta matrix. It is concluded that the main reason for the decrease in D is different for the Nb-rich and Ta-rich alloys: the hydrogen trapping for the former and a disturbance of tunneling jump for the latter.