Enhanced thermoelectric figure of merit in nano-structured Si dispersed higher manganese silicide

Higher manganese silicide (HMS) is considered as a promising thermoelectric material at intermediate temperatures. Samples of Si-rich HMS were prepared by arc melting followed by ball milling combined with densification by an induction hot uni-axial pressing (HP) and spark plasma sintering (SPS), respectively. Powder X-ray diffraction, SEM and EPMA studies confirmed the presence of Si in HMS matrix. TEM micrographs on milled powders further confirmed the presence of Si particles with an average size of similar to 5-10 nm in HMS matrix. Microstructure investigations on densified samples revealed that SPS process seems to be a beneficial tool for embedding the nanostructures of Si (similar to 20-50 nm) particles in HMS matrix. SPS also controls the grain growth of HMS during densification, which in turn reduces the total thermal conductivity from similar to 4.4 W/m.K to 2.10 W/m.K. On the other hand, samples processed by HP showed the value of similar to 2.44 W/m.K with similar sintering parameters as in SPS used for densification. Huge reduction in lattice thermal conductivity of about similar to 55%, and a considerable increase in Seebeck value was observed in Si-rich BMed HMS. However, reduction in electrical conductivity associated with insulating Si particles in HMS matrix limited the zT to similar to 0.26 at 725 K.