An investigation was made of the H diffusion behavior, at temperatures ranging from 300 to 20K, by using internal friction techniques. Pulse-echo high-frequency measurements were used in the high-temperature regime, while flexural vibrations were used in the low-temperature regime. Relaxation which was due to 2 types of H complex was observed. These were H-pairs and O- (or N-) H pairs. The H pair was shown to have an enthalpy of motion of 1.265kcal/mol and a binding enthalpy of 1.490kcal/mol. The O- (or N-) H pair was shown to consist of a single H atom which was bound to the O interstitial with an enthalpy of about 2kcal/mol. The enthalpy of H motion in the strain-field of the O atom was 3.900kcal/mol. The relaxations were shown to obey a classical Arrhenius temperature-dependence at high temperatures, and to exhibit enhanced relaxation rates at low temperatures.

C.Baker, H.K.Birnbaum: Acta Metallurgica, 1973, 21[7], 865-72

Figure 23

Diffusivity of H in Nb

Table 142

Parameters for H Diffusion in NbHx