Thermoelectricity and Thermal Conductivity in the Lead Sulfide Group of Semiconductors

The thermal conductivity and thermoelectric power of six specimens of PbS and one each of PbSe and PbTe have been measured at temperatures ranging from 4^∘{}K to 100^∘{}K. In the same temperature region the charge carrier mobility in these samples was determined from measurements of electrical resistivity and Hall coefficient. Four of the PbS samples were natural and n type, while the other specimens were synthetic and p type. The synthetic samples contained only a few single crystals but two of the natural specimens were highly polycrystalline.At low temperatures the charge carrier mobilities tend to high constant values similar to those reported elsewhere in single crystals of the same materials. From an estimate of the scattering cross section of the point defects we find evidence for explaining this behavior in terms of metallic rather than semiconducting properties.Maxima attributed to phonon drag have been observed below 20^∘{}K in the thermoelectric power of the specimens of highest thermal conductivity. The thermal conductivity was similar in all samples at 100^∘{}K but varied by as much as two orders of magnitude at 10^∘{}K. In order to explain these results it is necessary to consider scattering of phonons by point imperfections, free electrons, and dislocations.