Preparation And Thermoelectric Characteristics Of Mg2Si-Basic Bulk Nanocomposite

As one of the options for the energy conversion between thermal and electrical energy, thermoelectric(TE) materials are widely used in environmental, reliable and all-solid-state electricity generation and refrigeration. Magnesium Silicide is a kind of middle temperature thermoelectric material with the advantages of large effective carrier mass and mobility, abundant raw materials, low cost and environment friendly. For a decade or more, lots of theoretical studies have shown that low-dimensional TE materials could improve the thermoelectric properties remarkably. Thus the introduction of nanostructures is expected to improve the thermoelectric properties of Mg2Si-based alloys largely.In this paper, the low-temperature reaction method combined with the Field Activated and Pressure Assisted Synthesis process was used to successfully prepare MWCNTs, nano-SiO2and nano-La2O3doped Mg2Si based thermoelectric bulk nanocomposite. The effects of three types of nano-additives on the microstructure and thermoelectric properties of Mg2Si were studied. At the same time, the process of how to make the nano-additives disperse more homogeneously in Mg2Si matrix was improved.The electrical performance testing results of samples doped with SWCNTs indicate that the carbon nanotubes can improve the conductivity of the composites under low dosage. Among them, the sample with an addition of0.3wt.%SWCNT exhibits the best electrical property. Its power factor reaches1.09×10-3Wm-1K-2at the temperature of427K, which is higher than that of the sample without SWCENs (1.01×10-3Wm-1k-2). Both the addition of nano-SiO2and nano-La2O3improve the Seebeck coefficient of the composites. Lattice thermal conductivity decreases greatly as a result of the presence of the homogeneously dispersed nano-SiO2, which reduce the thermal conductivity of the composites largely and then enhance the thermoelectric properties. Among all of the samples,1wt.%SiO2/Mg2Si0.8Sn0.2exhibits the best figure of merit (ZT=0.25at573K), which is24%higher than that of the sample without SiO2. Thus, the adoption of low-temperature reaction and FAPAS method and the addition of nanometer-sized SiO2provide a new way of improving the thermoelectric properties of Mg2Si based materials.