Synthesis of Nanostructured Silicon - Germanium Thermoelectric Materials by Mechanical Alloying

Abstract: Silicon-germanium (SiGe) thermoelectric material is especially suited in power generation operating above 700 °C to 1000 °C to convert heat into electricity. Traditional bulk SiGe alloy thermoelectric materials has the value of dimensionless thermoelectric figure of merit (ZT) at maximum about 0.93 at 900 °C. It corresponds to 8% highest device efficiency to convert heat into electricity for commercial SiGe thermoelectric devices. Recently, many efforts have been made to increase the ZT value of SiGe thermoelectric materials. Among them, nanostructuring of SiGe alloy is an effective mechanism to enhance the ZT value of the thermoelectric material. In this approach, the ZT value increases due to the reduction of thermal conductivity caused by enhanced phonon scattering off the increased density of nanograin boundaries. There are different approaches to make nanostructured SiGe alloy bulk thermoelectric materials. Mechanical alloying of elemental Si and Ge powder is one of them. In this thesis work, different compositions of elemental Si and Ge micro powders have been mechanically alloyed using ball milling technique to produce SiGe alloy nanopowder and then were compacted and sintered by spark plasma sintering (SPS) method. Different characterization techniques have been used to see the effect of compositions, milling parameters and sintering conditions on the properties of the synthesized nanopowders and sintered compact samples.