Solid-State Synthesis of Mg_2Si_(1-x)Y_x(Y=Ge and Sn) Thermoelectric Materials via Bulk Mechanical Alloying

摘要

Magnesium base compounds and their solid solution have a promising potential as a thermoelectric material to be working in the middle-temperature range of 500 to 800K. In the present study, intrinsic Mg_2Si_(1-x)Y_x(Y=Ge and Sn; x=0, 0.2, 0.4, 0.6, 0.8 and 1.0) semi-conductive materials are successfully synthesized by the bulk mechanical alloying (BMA) at room temperature, starting from the elemental powder mixture. XRD and DTA techniques are used to describe the solid reaction process during BMA. The BMA specimens were further consolidated by the hot pressing (HP) at 773K by 1 GPa for 3.6ks for direct measurement of thermoelectric properties. Temperature dependence of the electrical conductivity, the Seebeck coefficient and thermal conductivity for both Mg_2Si_(1-x)Ge_x and Mg_2Si_(1-x)Sn_x were measured from the room temperature up to 700K. With increasing temperature, the electrical conductivity increased, the Seebeck coefficient and thermal conductivity decreased. The changes of the thermoelectric properties were also investigated for various Ge and Sn concentration. The thermoelectric properties were sensitive to the Ge and Sn concentration. The p-n conversion takes place at the vicinity of x=0.35 for Mg_2Si_(1-x)Ge_x and x=0.2 for Mg_2Si_(1-x)Sn_x. The figure of merit of Mg_2Si_(0.6)Ge_(0.4) in Mg-Si-Ge system reached 0.34 X 10~(-3) K~(-1) at 610K and Mg_2Si_(0.4)Sn_(0.6) in Mg-Si-Sn system reached 0.19 X 10~(-3)K~(-1) at 653K.