Structure and Thermoelectric Properties of Nanostructured Bi1−xSbx Alloys Synthesized by Mechanical Alloying

Abstract

We report on the synthesis of Bi1−xSbx alloys and the investigation of the relationship between their structural and thermoelectric properties. In order to produce a compound that will work efficiently even above room temperature, Bi1−xSbx alloys were chosen, as they are known to be the best suited n-type thermoelectric materials in the low-temperature regime (200 K). Using a top–down method, we produced nanostructured Bi1−xSbx powders by ball-milling in the whole composition range of 0 < x < 1.0. Nanostructuring of Bi1−xSbx alloys increases the band gap and thus results in an enlargement of the semiconducting composition region (0 ≤ x ≤ 0.5) compared to its bulk counterpart (0.07 ≤ x ≤ 0.22). The enhancement of the band gap strongly affects the transport properties of the alloys, i.e. the electrical conductivity and the Seebeck coefficient. Moreover, nanostructuring reduces the thermal conductivity through the implementation of grain boundaries as phonon-scattering centers, leading to a significant enhancement of the thermoelectric properties. The highest figure-of-merit observed in this study is 0.25 which was found for Bi0.87Sb0.13 at 280 K.