Thermoelectric and Thermomagnetic Transport in PbTe with Nanoscale Structures

Abstract

ABSTRACTQuantum-dot superlattices (QDSLs) have demonstrated thermoelectric figure of merit (ZT) values double those of classical bulk materials, providing the proof that nanoscale materials can address this age-old limitation on thermoelectric technology. Since QDSL materials can only be obtained in thin-film form, the development of bulk materials with nanoscale inclusions would be useful for many large-scale applications. Nanometer-scale inclusions in lead chalcogenides are known to improve the thermoelectric figure of merit through a combination of two factors: a strong decrease in lattice thermal conductivity, and an increase in the Seebeck coefficient over that of bulk PbTe for a given carrier concentration. This paper focuses on experimental results obtained on two types of PbTe nanocomposites, namely samples prepared by sintering powders with nanometer-sized grains, and samples prepared with nanoprecipitates of metallic Pb. The results are analyzed using the “method of four coefficients.” At each measurement temperature there are four unknowns. These are the carrier concentration, the mobility, the carrier effective mass, and the energy dependence of the relaxation time Tau, which is modeled by a power law: Tau proportional to energy to power Lamda. Therefore, at each temperature, four measurements are taken: the electrical conductivity, and the Hall, Seebeck and transverse Nernst-Ettingshausen coefficients. This analysis concludes that the effect of the nanoscale inclusions on the power factor is due to an increase in the scattering parameter λ, and that the nanoscale inclusions affect the electron scattering in such a way as to increase the Seebeck coefficient.