Influence of pulverization and GaO nanoparticles addition on thermoelectric properties and grain growth of Mg2Si based compound

Magnesium silicide is a promising eco-friendly thermoelectric material. Its constituent elements are non-toxic and exist in abundance on the earth. To improve thermoelectric performance of the material, reduction of thermal conductivity is required. In this study, we attempted to lower the thermal conductivity of A1-doped Mg2Si by milling of the powder and addition of calcium oxide nanoparticles (CONP). Grain size distribution and thermoelectric properties in the sintered samples were measured. Furthermore, influence of CONP addition on grain growth was investigated after heat treatment at 500 °C for 50 h in an argon gas. Milling process was effective enough to grain refining, but CONP addition had little effect on it. The milling treated samples lowered the thermal conductivity regardless of CONP addition. The milling treated sample without CONP addition had the best thermoelectric performance of ZT- 1.15 at 600 °C. The samples with CONP addition, however, resulted in degradation of thermoelectric performance at high temperature. The heat treatment brought to the grain growth for the sample without CONP addition and resulted in degradation of thermoelectric performance, while the sample with CONP addition controlled the grain growth after the heat treatment and maintained the thermoelectric performance.