Hydrogen in niobium under pressure

Abstract

By means of electrotransport and high precision electrical resistance measurements we studied the influence of hydrostatic pressure (up to 2.2 GPa) on the diffusion coefficient and some related properties of hydrogen in niobium. The hydrogen-to-niobium ratio was varied from 0.002 to 0.05 and the temperature from −80 to 160 °C. At atmospheric pressure the results for the diffusion coefficient are in accordance with the results from the Gorsky effect and quasi-elastic neutron scattering experiments. Even within the high precision of our measurements no change in the diffusion coefficient could be observed under hydrostatic pressure. This is in contradiction to theoretical predictions. Electrotransport measurements also provide information on the effective charge Z ∗ of the screened proton in niobium. Below 20 °C, Z ∗ increases rapidly with decreasing temperature. High pressure does not change Z ∗ and its temperature dependence. This must be due to a negligible influence of high pressure on the electronic structure of hydrogen in niobium. The specific electrical resistivity change due to dissolved hydrogen is not altered as a function of pressure. From this it is concluded that the lattice distortions due to hydrogen in niobium are not changed by high pressure.