Microstructure‐Lattice Thermal Conductivity Correlation in Nanostructured PbTe0.7S0.3 Thermoelectric Materials

Abstract

The reduction of thermal conductivity, and a comprehensive understanding of the microstructural constituents that cause this reduction, represent some of the important challenges for the further development of thermoelectric materials with improved figure of merit. Model PbTe‐based thermoelectric materials that exhibit very low lattice thermal conductivity have been chosen for this microstructure–thermal conductivity correlation study. The nominal PbTe 0.7 S 0.3 composition spinodally decomposes into two phases: PbTe and PbS. Orderly misfit dislocations, incomplete relaxed strain, and structure‐modulated contrast rather than composition‐modulated contrast are observed at the boundaries between the two phases. Furthermore, the samples also contain regularly shaped nanometer‐scale precipitates. The theoretical calculations of the lattice thermal conductivity of the PbTe 0.7 S 0.3 material, based on transmission electron microscopy observations, closely aligns with experimental measurements of the thermal conductivity of a very low value, ∼0.8 W m−1 K−1 at room temperature, approximately 35% and 30% of the value of the lattice thermal conductivity of either PbTe and PbS, respectively. It is shown that phase boundaries, interfacial dislocations, and nanometer‐scale precipitates play an important role in enhancing phonon scattering and, therefore, in reducing the lattice thermal conductivity.