Thermoelectric Properties of n-Mg₂(SiGe)_0.8Sn_0.2 Solid Solution

Abstract

High values of the thermoelectric figure of merit (ZT = 1.5) in Mg₂Si–Mg₂Sn solid solutions are caused by a low thermal conductivity and a complex band structure, which is optimal at the ratio of solid-solution components of 40% Mg₂Si and 60% Mg₂Sn. However, the presence of magnesium stannide in a high concentration impairs the mechanical properties and chemical stability of the material limiting its application at high temperatures. Magnesium silicide has a higher stability but a lower figure of merit. The figure of merit is much lower in Mg₂Si-rich solid solutions and amounts to ZT ~ 1. The possibility of increasing ZT in the Mg₂Si_0.8Sn_0.2 solid solution with the additional inclusion of Mg₂Ge in small quantities is investigated here. Samples of Mg₂(Si_{1 –x}Ge_x)_0.8Sn_0.2 (x < 0.03) solid solution are prepared by hot pressing. The temperature dependences of the coefficients of the thermoelectric power, electrical conductivity, and thermal conductivity are measured in the range of 300–800 K. An increase in the thermoelectric figure of merit to ZT = 1.1 is shown at T = 800 K in the Mg₂Si_0.78Ge_0.02Sn_0.2〈Sb〉 solid solution.