LATTICE THERMAL CONDUCTIVITY OF TA-NB AND NB-MO SOLID SOLUTION ALLOYS IN NORMAL AND SUPERCONDUCTING STATES

A detailed experimental investigation on the validity of the Bardeen-Rickayzen-Tewordt (BRT) theory for the ratio of the lattice thermal conductivity in the normal and superconducting states has been made for Nb-Mo and Nb-Ta alloys over a wide range of composition. The measured lattice ratios for the nine samples investigated are in complete agreement with the BRT theory down to reduced temperatures t similar 0·4. Below this temperature agreement is still obtained for the thicker samples; in thin samples deviations appear which are attributable to boundary or dislocation scattering. The variation of the lattice conductivity with composition has also been investigated. Addition of Mo to Nb noticeably increases the lattice conductivity, whereas addition of Ta to Nb has a much smaller effect. These results can be explained in terms of the variation of the electronic density of states N(0) with composition.