Suppression of grain growth by additive in nanostructured p-type bismuth antimony tellurides

Grain growth is a major issue in the preparation of nanostructured bismuth-antimony-tellurides during hot pressing the nanopowders into dense bulk samples. To prevent grain agglomeration during ball milling and growth during hot pressing, organic agent (Oleic Acid, OA) as additive was added into the materials at the beginning of the ball milling process. With different concentrations of OA (0.5, 1.0, 1.5, 2.0, and 2.5. wt%), grains with different sizes are obtained. Structural analysis clearly shows that it is the particle size of the nanopowders that determines the final grain size in the densely compacted bulk samples. A combination of small grains ~200-500. nm and nanopores leads to effective phonon scattering, which results in the decrease of lattice thermal conductivity, and ZT of ~1.3 at 373. K for the sample with 2.0. wt% OA.