Y.Q. Cao

Syntheses and thermoelectric properties of Bi2Te3∕Sb2Te3 bulk nanocomposites with laminated nanostructure

Nanocomposites with constituent sizes of <50nm are considered as a promising approach to enhance the figure of merit of bulk thermoelectric materials. A simple route involving hydrothermal synthesis and hot pressing was used in this work to prepare Bi2Te3∕Sb2Te3 bulk nanocomposites. It is shown that the composites have a laminated structure composed of Bi2Te3 and Sb2Te3 nanolayers with the thickness varying alternately between 5 and 50nm. The transport measurements indicate that the nanoscale laminated structure improves the thermoelectric performance with the maximal dimensionless figure of merit of 1.47 for the nanocomposite hot pressed from Bi2Te3 and Sb2Te3 nanopowders.

Low thermal conductivity and improved figure of merit in fine-grained binary PbTe thermoelectric alloys

Fine-grained binary PbTe thermoelectric materials have been fabricated by a combination of a reflux chemical synthesis and hot pressing. The grain sizes of the hot pressed bulk samples varied from 200 to 400 nm, which significantly contributed to the thermal conductivity reduction due to the enhanced phonon scattering at grain boundaries. Low room temperature thermal conductivity of 0.75 W m−1 K−1 has been obtained after porosity correction for the sample with a grain size of ~200 nm. The highest figure of merit ZT of the fine-grained binary PbTe bulk sample reaches 0.8 at 580 K although the composition was unoptimized. The value is comparable to that of the best PbTe alloys.

Nanostructuring and thermoelectric properties of semiconductor tellurides

Bulk nanostructured (Bi,Sb)2Te3 compounds and GeTe based amorphous/nanocrystal composites have been successfully fabricated by the combined hydrothermal/hot-pressing and quenching/annealing methods, respectively. The (Bi,Sb)2Te3 nanopowders synthesized by hydrothermal method exhibit a hollow-like structure. After hot-pressing, the nanoscale grains varying from tens to hundreds of nanometers were found in the bulk sample. The maximum ZT value of this (Bi,Sb)2Te3 sample is higher than the zone-melt one at room temperature. The sizes of the nanocrystals in the bulk GeTe nanocomposites were below 10 nm, the presence of which contributed to the remarkable improvement of the electrical conductivity and thermoelectric power factor compared to the amorphous precursors.