Thermoelectric properties of binary Mg₂Sn and ternary Mg₂Sn_1−xY_x (Y = Si, Ge) with the addition of Cu₂S

Doped and undoped ternary and binary Mg₂Sn solid solutions were fabricated using high-energy ball milling followed by hot pressing according to the nominal Mg₂Sn_1−xY_x (X = 0, 0.25 and Y= Si, Ge) composition with the addition of 20 at% of Cu₂S. The effects of Cu₂S addition on the thermal conductivity, Seebeck coefficient and electrical conductivity were investigated in the temperature range of 300–800 K. It was found that the Cu₂S addition increased both the electrical conductivity and Seebeck coefficient simultaneously, which is unusual in thermoelectricity, leading to enhancement of the power factors. Additionally, the addition of Cu₂S significantly decreases the thermal conductivity. It was also observed that the ternary compositions (i.e. compositions containing Si, Ge) results in a high power factor as a result of the combined optimized Seebeck coefficient and electrical conductivity. This is as a result of phase separations into SnS and Mg₃Sb₂ phases, which are enhanced by the addition of Si and Ge. Overall, the ZT values significantly improved to 1.35 at 700 K and 1.3 at 750 K for Si and Ge ternary samples, respectively.