Low-Temperature Thermal Conductivity of Boron

The thermal conductivity of a single crystal of boron has been measured between 4 and 300°K. The crystal structure is beta-rhombohedral, and the Debye temperature 1200°K. An exponential temperature dependence, $e{\Theta }^{/aT}$, was observed in the neighborhood of 150°K; the value of $a$ was 2.4. This temperature dependence is characteristic of umklapp processes. The maximum conductivity is approximately 3 W/cm deg near 50°K. At low temperatures the conductivity obeys a $T^{1.8}$ law and has a magnitude one tenth that expected for boundary scattering. The latter effect may be associated with the presence of dislocations. The data are analyzed by the phenomenological model of Callaway.