Bulk electro- and thermotransport in Nb

Similar to Vanadium Nb belongs to the anomalous transition metals with a curved Arrhenius line for the temperature dependence of diffusion. For thermotransport in V different transport mechanisms for lower and higher temperatures were found. In our measurements of the electro- and thermotransport in Nb we observed some irregular disturbances of the marker movement probably from a precipitation of vacancies into voids. From less disturbed measurements we got the following results. - The thermotransport is directed to the cold end i.e. the heat of transport Q* is positive. In the range from 1540 to 2240 degrees C we assume two activation energies, energies, Q(T1)=3.5-4.1eV for the higher (HT) and Q(T2)=2.5-3.2eV for the lower temperature (LT). The energy ranges indicate individual sample behaviour The corresponding Q* values are Q(1)*=1.9+/-0.8eV and Q(2)*=4.6+/-0.7eV. The activation energies are lower than the activation energies for selfdiffusion (Q(D1)=4.59eV and Q(D2)=3.67eV). We suggest that this is due to a contribution of dislocations while the main mechanism is a vacancy mechanism as in diffusion. - For electrotransport we obtain a positive effective charge number z*=3.2+/-1.4 i.e. the transport is directed to the cathode. There was a single activation energy Q(E)=3,0...3,7 eV in the investigated range from 1540 to 2240 degrees C.