Modified polyol synthesis of bulk-scale nanostructured bismuth antimony telluride

Bismuth antimony telluride, Bi0.5Sb1.5Te3, is a prototype thermoelectric alloy for which nanostructuring has been shown to improve the thermoelectric figure of merit. Most bulk-scale nanostructured thermoelectric materials are synthesized using either traditional solid-state routes or “top-down” physical methods such as ball milling, sputtering, etc. “Bottom-up” chemical methods represent an important alternative route to nanostructured thermoelectrics, but often produce small sample sizes that make transport measurements difficult. Here, nanostructured Bi0.5Sb1.5Te3 has been synthesized in half-gram quantities using a simple and scalable modified polyol process. Stoichiometric amounts of appropriate metal salts were combined in tetraethylene glycol with and without poly(vinylpyrrolidone) (PVP), reduced with sodium borohydride, and heated in solution and in powder form to obtain samples of crystalline Bi0.5Sb1.5Te3. The structure, composition, and morphology of the products were characterized using powder XRD, TEM, SEM, and EDS mapping data. The Seebeck coefficient, measured from 300-500 K for 1 cm sintered pellets of Bi0.5Sb1.5Te3, increased with temperature and was found to be +256 µV K−1 at 500 K. Bulk-scale nanostructured powders of other thermoelectrics could also be synthesized, including Bi2Te3, PbTe, Sb2Te3, AgSbTe2, and Pb1−xSnxTe