Influence of Pulverization and CaO Nanoparticles Addition on Thermoelectric Properties and Grain Growth of Mg₂Si Based Compound

抄録

Magnesium silicide is a promising eco-friendly thermoelectric material. Its constituent elements are non-toxic and exist in abundance in the Earth's crust. To improve thermoelectric performance of the material, reduction of thermal conductivity is required. In this study, we attempted to lower the thermal conductivity of Al-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 ℃ for 50 h in an argon gas atmosphere. Milling process was effective enough to grain refinement, but CONP addition had little effect on it. The thermal conductivity was reduced in the milling treated samples regardless of CONP addition. The milling treated sample without CONP addition had the best thermoelectric performance of ZT = 1.15 at 600 ℃. 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 inhibited the grain growth after the heat treatment and maintained the thermoelectric performance.