PbTe-PbSnS ₂ thermoelectric composites: Low lattice thermal conductivity from large microstructures

Recent advances in the field of thermoelectrics have shown embedding appropriate nanostructures can significantly suppress the lattice thermal conductivity and therefore enhance ZT. Here we report a new class of thermoelectric composites of PbTe-PbSnS ₂. PbSnS ₂ is a naturally layered material (space group Pnma) comprised of Sn-Pb bilayers approximately 0.6 nm in thickness. High resolution transmission electron microscopy reveals the PbSnS ₂ segregates into coherent lamellar structures 50-100 nm in thickness that extend 100 nm to 15 μm in length. Despite the relatively large size of the PbSnS ₂ precipitates, we find that incorporation of PbSnS ₂ in PbTe results in significant reduction in lattice thermal conductivity to 0.4-0.65 W m ^-1 K ^-1 over the temperature range 300-700 K, a reduction of 50-70% over bulk PbTe. As a result, a maximum ZT of 1.1 is obtained for ingot samples of the PbTe-PbSnS ₂ 6% composition. We provide extensive characterization of the physical, structural, and chemical properties of this materials system including powder X-ray diffraction, infrared reflectivity, scanning and transmission electron microscopy, and thermoelectric properties measurements. The synthesis method is simple and general, opening possibilities for similar systems to yield materials exhibiting low lattice thermal conductivity without it being necessary to embed nanoscale (5-20 nm) features.