Fabrication of Mg 2 Si from a Reused-silicon Source and its Thermoelectric Characteristics
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1044-U06-15
Fabrication of Mg2Si from a Reused-silicon Source and its Thermoelectric Characteristics Masayasu Akasaka1,2, Tsutomu Iida1, Youhiko Mito3, Takeru Omori1, Yohei Oguni1, Shigeki Yokoyama3, Keishi Nishio1, and Yoshifumi Takanashi1 1 Department of Materials Science and Technology, Tokyo University of Science, 2641 Yamazaki, Noda-shi, Chiba, 278-8510, Japan 2 Research Fellow of the Japan Society for the promotion of Science, Tokyo, 102-8472, Japan 3 Showa KDE Co.,Ltd., 30-13, Motoyoyogi-cho, Shibuya-ku, Tokyo, 151-0062, Japan ABSTRACT Polycrystalline Mg2Si was fabricated from a reused-Silicon source, based on Si sludge, using Plasma Activated Sintering technique. The n-type and p-type dopants, bismuth (Bi) and silver (Ag), respectively, were incorporated into the Mg2Si. The thermoelectric properties were estimated from 300 to 873K. The power factors of undoped and Bi-doped samples from the reused-Si source were comparable to those from a solar grade Si source (99.99999%). The power factor was estimated to be 2.5 x 10-5 W/cmK2 for the Bi-doped sample from the reused-Si source. However, the power factor of the Ag-doped, p-type sample from the reused-Si source was lower than that from solar grade Si source. The dimensionless figures of merit of samples from the resused-Si source were slightly lower than those from a solar grade Si source. The dimensionless figure of merit was estimated to be 0.53 at 812 K for Bi-doped sample from the reused-Si source. INTRODUCTION The anticipated global average of surface warming noted in the 4th Assessment Report from the Intergovernmental Panel on Climate Change (IPCC) was revised to be up by 6.4 degrees centigrade by 2100 [1]. In order to reduce Greenhouse effect gases, which mostly cause global warming, high-efficiency utilization of fossil fuel is required, along with a prevailing employment of reusable energy sources, such as solar cells. 70 % of the combustion energy of fossil fuel is wasted as unused heat energy [2]. Therefore, to enhance the efficiency by recycling the unused heat energy occupies an important place in the solution to global warming. Thermoelectric power generation is able to directly convert heat energy into electrical power, which is the most convenient form of energy to use in modern society. Magnesium silicide (Mg2Si) has been identified as a promising advanced thermoelectric material, operating in the temperature range from 500 to 800 K [3-5]. Compared with other thermoelectric materials that operate in the same conversion temperature range, such as PbTe and CoSb3, several important characteristics of Mg2Si have been identified, including that it is an environmentally-friendly material, that its constituent elements are abundant in the earth’s crust, and that it is non-toxic. In order to realize thermoelectric devices that are based on Mg2Si, together with improvements in its thermoelectric properties, cost reductions of the source materials and manufacturing processes are also required. Silicon, as a component of Mg2Si, is a substrate material fo
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