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The influence of nitrogen impurities on the diffusion coefficient of hydrogen in niobium has been measured with the help of the Gorsky-effect technique. The data can be interpreted as if nitrogen in Nb suppresses the fast low-temperature diffusion process.

Reports on Gorsky effect measurements in which diffusion was investigated in the presence of N interstitial defects. Points out that the temperatures were between 120 and 450 K, and the H(D) and N concentrations ranged up to 1 at%. Results show a decrease of the H(D) diffusivity in the presence of N impurities, and that H diffusion at low temperatures is reduced. Proposes that the experimentally observed reduction of the relaxation strength can be attributed either to trap saturation, or to a dipole-moment tensor smaller for trapped than for free hydrogen. Concludes that under consideration of the arbitrariness involved in any specific trap model (e.g. existence of shallow traps with different dipole-moment tensors and binding enthalpies), and under consideration of the precision of our data, it is not possible to decide to what extent each one of these 2 effects is responsible for the N-induced decrease of relaxation strength.

Experimental results are reported for the resistivity variations which are caused by interstitial hydrogen in V, Nb and Ta. The results include data for the two hydrogen isotopes H and D, so that the isotope dependence of the resistivity variations could be studied systematically for all three metals.

Schaumann et al. [Phys. Stat. Sol. 42: 401(1970)] have reported measurements of the diffusion coefficient of H in Nb by means of the Gorsky effect over the temperature range of -150 to +300$sup 0$C. In this temperature range a marked change of the slope in an Arrhenius plot from U = 0.106 eV for T greater than 20$sup 0$C to U = 0.068 eV for T less than -50$sup 0$C has been observed. The high-temperature value has been confirmed by R. Cantelli et al. [Phys. Stat. Sol. 34: 597(1969)]. The change in slope has been reproduced by Wipf and Alefeld [Phys. Stat. Sol. 23: 175(1974)] with a resistivity technique simultaneously showing that the change does not exist for deuterium in niobium. Munzing et al. [Scripta Met. 8: 1327(1974)] report that the low-temperature process disappears gradually on alloying with small amounts of nitrogen. In a recent paper by Matusiewicz et al. [Scripta Met. 8: 1426(1974)] these results concerning the change in activation energy have been questioned on the basis of new Gorsky-effect measurements. It is noted that measurements confined to the transition region are not very likely to reveal a change in slope as a function of temperature. In the transitionmore » region the apparent activation energy is an average between the high-temperature and low-temperature value. The apparent activation energy in the transition region increases. (auth)« less