Recent Studies on the Environmentally Benign Alkaline-Earth Silicide Mg2Si for Middle-Temperature Thermoelectric Applications

Most primary energy sources, such as the fossil fuels of oil, coal, and natural gas, produce waste heat. Recycling of this unused thermal energy is necessary in order to increase the efficiency of usage. Thermoelectric (TE) conversion technologies, by which waste heat is directly converted into electricity, have been extensively studied, and the development of these technologies has continued. TE power-generation has attracted significant attention for use in self-powered wireless sensors, which are important for our increasingly sophisticated information society. For the middle-temperature range (i.e., 600-900 K), with applications such as automobiles, intensive studies of high-performance TE materials have been conducted. In this study, we review our recent experimental and theoretical studies on alkaline-earth silicide Mg2Si TE materials, which consist of nontoxic abundant earth elements. We demonstrate improvements in TE performance brought about by lightly doping Mg2Si with isoelectronic impurities. Furthermore, we examine the electrode formation and material coatings. Finally, we simulate the exhaust heat requirements for the practical application of TE generators.