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1102-LL04-30

Thermoelectric High Power Generating Module made by n-Ba8AlxSi46-x Clathrate Shinji Munetoh, Makoto Arita, Hideki Makiyama, and Teruaki Motooka Department of Materials Science and Engineering, Kyushu University, 744 Motooka, Fukuoka, 819-0395, Japan ABSTRACT We have developed a new thermoelectric power-generating module composed of 72 pieces of n-type Ba8Al18Si28 clathrate elements made by arc melting. The Seebeck coefficient, specific electric resistance and thermal conductivity of Ba8Al18Si28 clathrate were 250 µV/K, 1.9 mΩcm and 3.1 W/mK at 500 ºC, respectively, and the thermoelectric figure of merit (ZT) was 0.8. The new thermoelectric module was constructed using only n-type thermoelectric elements connected in series with hook-shaped electrodes. The open-circuit voltage of the module was 1.8 V at the hot-side temperature of 500 ºC. The maximum electric power was 0.24 W. The module was successfully used to charge lithium-ion batteries for mobile phones. INTRODUCTION Automobiles and garbage furnaces release waste heat which equals to about 70 % of the total energy. Thermoelectric power generation as a method of recovering the waste heat from the heat sources is one of the most important technology in view of fossil fuel exhaustion. Since the middle of the twentieth century, thermoelectric materials, Bi-Te, Pb-Te, and Si-Ge [1,2,3] are used for thermoelectric power generation in military and aerospace. However, these materials have some problems such as low melting point, harmful or expensive elements for practical applications. Recently, many materials for high efficiency thermoelectric power generator have been researched [4,5]. Slack has proposed a new criterion for high efficiency thermoelectric materials and it is argued that cage compounds with a large unit cell containing encapsulated atoms which "rattle'' inside the voids will have a low thermal conductivity [6,7]. Silicon clathrate compounds have been investigated as a high efficiency thermoelectric material with low lattice thermal conductivity due to "rattling" of atoms that fill in voids in the crystal structure [8]. Thermoelectric module is normally composed of an array of thermoelectric couples joined n- and p-type semiconductor materials. However, no p-type material has been obtained for silicon clathrates. In this study, we synthesized n-type Ba8Al18Si28 clathrate by arc melting and prepared a thermoelectric power generator composed of only n-type Ba8Al18Si28 clathrate. EXPERIMENT Thermoelectric elements were prepared using Ar arc melting. 8:18:28 molar mixtures of Ba, Al, and Si were melted in an Ar-arc furnace. Subsequently, the samples were annealed at 850 ºC for 20 hours in a vacuum (10-3 Torr) as a solution treatment. Thermoelectric elements with a size of 5 x 5 x 8 mm3 were cut from the annealed samples. The thermoelectric elements, 72 pieces, were inserted into the Al2O3 meshes formed on the brass substrate for electrical contact in series with hook-shaped electrodes. The thermoelectric elements were connected to the electrode