Experimental and theoretical evaluation of the phonon thermal conductivity of niobium at intermediate temperatures

The thermal conductivity, electrical conductivity, and thermopower of Nb and four Nb-based alloys were measured over the temperature range 80-400 K. The thermal- and electrical-conductivity data were used to define the roles of phonon-phonon and phonon-electron scattering in limiting the phonon thermal conductivity. The phonon-electron thermal resistance was compared with the results of a new first-principles calculation. As expected from the high superconducting transition temperature, phonon-electron scattering is quite strong in Nb. The theoretical calculation reproduces the results of an earlier low-temperature experiment, but gives only about $\frac{2}{3}$ of the scattering strength derived from the intermediate-temperature data. This discrepancy is just inside the experimental error limits, but some possible explanations of the difference are discussed.