Abstract: As one of the most potential medium temperature thermoelectric materials, Mg2Si1-xSnx -based alloy has received widely attention due to the advantage of low cost and non-toxic. Lattice thermal conductivity of ternary Mg2Si1-xSnx alloys is reduced, because alloying scattering is enhanced by the large mass difference of elements. The minimum of thermal conductivity is 1.8 W·m-1·K-1, and it well resolves the disadvantage of high thermal conductivity for Mg2Sn binary alloys. However, the main methods to optimize the thermoelectric properties of Mg2Si1-xSnx alloys are decreasing the grain size to further reduce the thermal conductivity. But the performance of this kind of thermoelectric device is prone to degradation due to the grain growth in high temperature service. Therefore, improving the power factor by the method of doping and band engineering is a more reliable way to optimize the thermoelectric performance. In this paper, electronic structures analysis and thermoelectric properties prediction has been made to the Mg2Si1-xSnx (0.25≤x≤0.75) compounds by first principle calculation method. The calculated band structures in Mg2Si1-xSnx show the conduction band convergence directly. This convergence in energy at x=0.625 can enhance the Seebeck coefficient of the solid solution without influencing the electrical conductivity. The Seebeck coefficient and power factor of Mg2Si0.375Sn0.625 could reach -246 μV·K-1 and 6.2 mW·m-1·K-2, respectively, at the optimal doping density of 3×1020 cm-3. The predicted and tested results of ZT maximum are 1.3 and 1.16 at T=700 K, respectively. In the medium temperature range of 550—800 K, the predicted and tested ZT values can keep above 1.0 and 0.9, respectively. Therefore, power factor optimization is an effective way to improve the thermoelectric properties of Mg2Si1-xSnx crystal.
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