Nanostructured bulk thermoelectric materials and their properties

Advanced bulk thermoelectric materials have been developed by fabricating composites of uniformly distributed thermoelectric nanoparticles within a high surface area semiconductor matrix. In this composite structure, constituents of the thermoelectric materials´ figure of merit can be decoupled and controlled independently, and consequently, one can achieve a high thermoelectric figure of merit. The produced composites exhibited extremely low thermal conductivity and relatively high electrical conductivity. However, the Seebeck coefficient was relatively low, probably due to poor quality of the thermoelectric particles. In an in-plane test geometry (van der Pauw configuration), the electrical resistivity of the composite sample decreased continuously as temperature increased, a typical semiconductor behavior. In the perpendicular-to-the-plane (cross-plane) test geometry, electrical resistance of the sample increased continuously with increasing temperature, probably a semi-metallic behavior. This anisotropy in the electrical resistance was reproducible. We also observed relatively strong high frequency AC-signals in the in-plane test geometry samples.