Solid-state synthesis of Mg₂Si_1-xY_x(Y=Ge and Sn) thermoelectric materials via bulk mechanical alloying

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 Mg₂Si _1-xY_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 Mg₂Si_1-xGe_x and Mg₂Si_1-xSn_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 Mg₂Si_{1- x}Ge_x and x=0.2 for Mg ₂Si_1-xSn_x. The figure of merit of Mg ₂Si_0.6Ge_0.4 in Mg-Si-Ge system reached 0.34 × 10^-3K^-1 at 610K and Mg₂Si _0-4Sn_0.6 in Mg-Si-Sn system reached 0.19 × 10 ^-3K^-1 at 653K.