Nanostructured Thermoelectric Composites

NanoLab, Boston College and MIT conducted a Phase I development effort in nanoscale thermoelectric composites. Our goal was to show that the high ZT obtained for quantum dot structures can also be obtained using scalable nanoparticle processes. The research focused on the synthesis of nanoscale lead selenide (PbSe) and lead telluride (PbTe). Next, densification procedures were developed with micron scale powders, then with nanopowders. We achieved near theoretical densities, but saw grain growth. MIT first tested parts made from micron scale powders, which showed expected values for thermal & electrical conductivity. Next, MIT tested parts made from nanoscale powders. For nanoscale PbSe, the electrical conductivity increased to 72,690 S/m. However, the thermal conductivity also increased to 2.12 W/mK, so ZT was ~0.32. We attribute the high thermal conductivity to sub-optimal thermal processing conditions. Similar work was conducted for PbTe, but the nanoscale PbTe had a lower electrical conductivity (15,469 S/m) than its micron scale counterpart (25,614 S/m). We achieved lower thermal conductivity (1.66 vs. 1.8 W/mK), but overall, the ZT stayed near ~0.2. Like PbSe, thermal processing optimization can improve performance. In Phase II, we plan to optimize the densification, then mass produce high ZT nanostructured thermoelectric materials.