A study of the low temperature transport properties of molybdenum and tungsten alloys using a SQUID picovoltmeter

Measurements of the electrical resistivity and the thermoelectric function have been made on dilute W-Ta, Mo-Nb and Ta-W alloys in the temperature region 1K to 7K. The measurements were made using a SQUID picovoltmeter, which, at best, had a sensitivity of about 1 pV. It was found that several anomalies occurred in both the resistivity and thermoelectric function of the W-Ta and Mo-Nb alloys. Their exact cause is uncertain: the anomalies in the Mo-Nb alloys are probably due to a magnetic impurity, while those of the W-Ta alloys may, in fact, be an intrinsic effect. More experimental work needs to be done in order to verify this. With perhaps a few modifications, it was possible to describe the normal behaviour of both the resistivity and thermoelectric function in terms of present understanding of transition metals and alloys. The resistivity could, for the main part, be interpreted in terms of a T2 electron-electron scattering term and a T4 electron-phonon scattering term, the latter contradicting the T5 Bloch-Gruniesen Law. The thermoelectric function could be adequately described by a temperature independent diffusion component and a T2 phonon drag term. (author)