Preparation Of Mg₂Si Based Thermoelectric Nanomaterals By Low-temperature Chemical Reaction

As a kind of functional material which can convert heat into electricity directly, thermoelectric material is of promising application value for thermoelectric generation and thermoelectric cooling. The thermoelectric devices own some advantages such as pollution-free, noiseless, maintainable and safe, are novel green energy resources. Magnesium silicide is a kind of middle temperature thermoelectric material, owns some advantages such as the large effective carrier mass and mobility, abundance of its raw materials, low cost and environment friendly.lt’s generally considered that the method of reducing the grain size to the micron and even nanoscale can significantly reduce the thermal conductivity of Mg2Si.In this paper, the method of MgH2powder reaction was used to prepare high-purity Mg2Si, which is an effective way to avoid the generation of MgO impurity. The partial pressure of hydrogen produced by reaction can further reduce the oxygen content in the product. The method of field-activated and pressure-assisted synthesis(FAPAS) combined with low-temperature reaction was used to realize the rapid reaction and densification of high-purity Mg2Si based thermoelectric nanomaterials and the reaction process has been optimized. Mg-Si-Sn based thermoelectric materials doped with rare earth (RE) Pr were prepared. The advantages of new process were comparatively studied.Three series of samples of high purity and good crystallinity were prepared. The average grain size of all samples was about50nm. Nanocrystals can significantly reduce the thermal conductivity, thereby enhance the thermoelectric properties. The thermal conductivity and ZT value of high-purity nano-Mg2Si sample are3.5μV/K and0.20, which are respectively40%and1.11times of that of the traditionally prepared samples. High-purity products can be obtained in one step by adopting the method of Mg2H reaction. The grain size is about56.7nm. The thermal conductivity at800K is2.3Wm-1k-1, which is57%of that of the traditionally prepared sample. The ZT value at800K is about0.33, which is1.6times of that of traditionally prepared sample. Pr doping can effectively improve the electric conductivity of thermoelectric materials and improve the ZT value. The ZT value of sample doped with Pr(0.2%) is1.5times of that of none-doped sample.