Dependence of thermal conductivity on electrical resistivity in Bismuth-Tellurides

The p-type (Bi0.25Sb0.75)2Te3 doped with 3-12 wt% excess Te alone and n-type Bi2(Te0.94Se0.06)3 codoped with 0.017-0.026 wt% Te and 0.068-0.102 wt% I were prepared by the Bridgman method, to produce intentionally polycrystalline. Some of the as-grown specimens were annealed, in order to prepare specimens with much different ρ. These polycrystalline specimens have almost the same degree of alignment of the c plane parallel to the freezing direction. The electrical rersistivity ρ and thermal conductivity κ were measured at 298 K along the freezing direction and κ was plotted as a function of ρ. As a result, the lattice components κph obtained by subtracting the electronic component κel from the observed κ were found to decrease almost linearly with a decrease of ρ in both p- and n-type specimens, where κel was calculated using Wiedemann-Franz law. This tendency is consistent with the conventional result that κph becomes negligible small in metals. The significant decrease in κph with decrease in ρ is considered to be caused predominantly by the phonon scattering due to dopants. The relationship between κph and ρ was first clarified in the intermediate region between the metal and insulator.