Significant Enhancement of the Thermoelectric Performance of Higher Manganese Silicide by Incorporating MnTe Nanophase Derived from Te Nanowire

Higher manganese silicide (HMS) is a naturally abundant, eco-friendly, and low-cost p-type thermoelectric semiconductor with high power factor (PF); however, its figure of merit (ZT) is very low due to an intrinsically high thermal conductivity (K). It is also difficult to synthesize a HMS single phase without MnSi or Si second phase, which generally leads to a significant decrease of the PF and/or increased K. In this study, pure HMS was obtained via wet ball milling in combination with spark plasma sintering. A further p-type MnTe, with high Seebeck coefficient (S) and low K, was incorporated into the HMS matrix to form MnTe/HMS composites. To effectively decrease K, while simultaneously enhancing the electrical conductivity, Te nanowires of similar to 35 nm in diameter were synthesized with a solution phase method and subsequently embedded to HMS to form MnTe/HMS nano/bulk structures. The incorporation of Te nanowires led to a 38% reduction of K in addition to a slight increase of S. Finally, the ZT(max) of MnTe/HMS nano/bulk composites increased by similar to 71% from 0.41 to 0.70. This study demonstrates a unique and facile method to boost the ZT of HMS to a high level, which is also applicable to other thermoelectric materials.