Nanostructured Thermoelectric Materials: Stoichiometric and Non-Stoichiometric Nanostructures in Hot Pressed Bi2Te2.7Se0.3

The purpose of our research in thermoelectric materials and devices is to understand nanostructural features in thermoelectric materials and design nanostructures to enhance the figure of merit, which is determined by its electrical conductivity, the Seebeck coefficient (S) and the thermal conductivity. Recent transmission electron microscopy investigation of as-pressed and re-pressed Bi2Te2.7Se0.3, a promising room temperature thermoelectric material, revealed disordered stoichiometric nanorods and ordered off-stoichiometric nanoparticles.

Use of multiple TEM techniques, including bright/dark field diffraction contrast imaging, electron diffraction and high resolution TEM, revealed a network (period ~10nm) of crystalographically aligned disordered/amorphous nanorods with the same composition in every grain. It is very likely that this nanostructure is responsible for the low thermal conductivity that makes Bi2Te3-system materials such attractive thermoelectric materials. The nanoparticles have Bi2Te3 crystal structures that accommodate Bi-enrichment by inserting additional Te-Bi- and Bi-Bi layers. Better understanding of these nanoparticles could be used to further reduce thermal conductivity or inhibit grain growth in Bi2Te3-system materials.