LATTICE THERMAL CONDUCTIVITY OF SUPERCONDUCTING NIOBIUM CARBIDE

The unusually low lattice thermal conductivity of the transition-metal carbides at low temperatures has been attributed to the scattering of phonons by conduction electrons. An experiment which confirms this interpretation is reported. Thermal conductivity measurements on single-crystal NbC0.96 through its superconducting critical temperature (9.8°K) show that the lattice component of the thermal conductivity, Kl3, increases greatly below Tc because of decreased phonon-electron scattering. The maximum increase in lattice thermal conductivity from this effect occurs at 3°K with KlsKln equal to 160. The theories of Bardeen, Rickayzen, and Tewordt and of Klemens and Tewordt for the influence of electrons and point defects on lattice conductivity provide a quantitative interpretation of the effect. The best fit to the NbC0.96 data is for 2ε(o)kTc=4.0. The behavior of NbC0.96 is in contrast to that of NbC0.76, which remains in the normal state throughout the temperature interval studied and shows no increase in thermal conductivity. © 1969 The American Physical Society.