Power Factor Optimization and Thermoelectric Properties of Mg2Si1-xSnx Alloys by Directional Solidification

Single-phase Mg2Si1-xSnx crystal was directionally solidified from the melt. The thermoelectric properties were tested for 1.5 at% Bi-doped crystals with different Sn contents, and the electronic transport properties were predicted by the first-principle calculation. At x=0.625, tested Seebeck coefficient and power factor are -247 μV•K-1 and 5.7 mW•m-1•K-2, respectively, because the band structure of Mg2Si0.375Sn0.625 is converged. This result is consistent with the calculated values, and the power factor is enhanced by 25%. 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 0.9. Power factor optimization is an effective way to improve the thermoelectric properties of Mg2Si1-xSnx crystal. In addition, the performance deterioration of thermoelectric devices induced by nano-sized grain growth at high service temperature can be avoided. © 2020, Science Press. All right reserved.