Thermoelectric Properties of NaZn 13 -type Intermetallic Compounds
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S8.23.1
Thermoelectric Properties of NaZn13-type Intermetallic Compounds Y. Amagai1, 2, A. Yamamoto2, C. H. Lee2, H. Takazawa2, T. Noguchi2, H. Obara2, T. Iida1, and Y. Takanashi1 1 Department of Material Science and Technology, Tokyo University of Science (TUS), Japan 2 Energy Electronics Institute, National Institute of Advanced Industrial Science and Technology (AIST), Japan ABSTRACT We report the electrical resistivity and the Seebeck coefficient of AZn13 (A = Sr, Ba, and La) and LaCo13 measured over a wide temperature range and their thermal conductivity measured at room temperature. The electrical measurements of AZn13 and LaCo13 above room temperature reveal that the compounds show good metallic behavior. We find that the absolute value of Seebeck coefficient for AZn13 (A = Sr, Ba, and La) increases with increasing temperature, which is a typical metallic behavior and the absolute value is less than 3µVK-1 at room temperature. Accordingly, the power factor of AZn13 is quite low. Temperature dependence of the Seebeck coefficient for LaCo13 is similar to that of Co. The absolute value of the Seebeck coefficient for LaCo13 is high as a metallic conductor and approaches -30µVK-1 at 500K, which leads LaCo13 to large power factor of 1.8 x 10-3Wm-1K-2. We obtained lattice components of the thermal conductivity by subtracting electronic contributions from the total thermal conductivity. The electronic components of the thermal conductivity were estimated using Wiedemann-Frantz law assuming L (Lorentz number) is 2.45 x 10-8 V2K-2. The thermal conductivities of the lattice components for AZn13 (A = Sr, Ba, and La) and LaCo13 with NaZn13 type structure are about 10 Wm-1K-1, respectively. These values are high as compared with other thermoelectric materials. INTRODUCTION Thermoelectric power generation system using intermetallic semiconductor device can directly convert thermal energy into electrical energy and desirable materials used in the device is called as thermoelectric materials. The thermoelectric conversion system is expected to play an important role in converting exhausted heat into electrical energy. Successful commercial applications of the thermoelectric power generation depend to a large degree in increasing the figure of merit Z defined by the following equation.
α2 ρ (κ e + κ l ) α2 P= ρ Z=
(1) (2)
where α, ρ, κe, κl, and P are the Seebeck coefficient, the electrical conductivity, the thermal conductivity, the electrical and lattice components of thermal conductivity and the power factor. One of the criteria for application of thermoelectric materials can be expressed ZT ≥ 1, where T is the absolute temperature.
S8.23.2
Thermoelectric materials should possess large electrical conductivity and Seebeck coefficient, and very low thermal conductivity like a glass to maximize figure-of-merit Z. Indeed, Bi2Te3 [1] and its alloys which are extensively employed in refrigeration possess the low thermal conductivity of 1.5Wm-1K-1 and show the highest figure-of-merit of ZT~1. In order to achieve low thermal
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