Understanding Electrical Transport and the Large Power Factor Enhancements in Co-Nanostructured PbTe

We previously reported the synthesis of nanostructured composite PbTe with excess Pb and Sb metal inclusions. The electrical conductivity shows an unusual temperature dependence that depends on the inclusion Pb/Sb ratio, resulting in marked enhancements in power factor and ZT at 700 K. Additional investigation of the transport and structure of these materials is reported here. Measurements of the scattering parameter reveals there is little change in electron scattering with respect to pure PbTe. High resolution electron microscopy was used to determine additional information about the nature of the precipitate phases present in the samples. High temperature transmission electron microscopy reveals that the precipitates begin to dissolve at high temperatures and completely disappear at T > 619K. A qualitative explanation of the unusual transport behavior of these materials is presented.