Thermoelectric properties of the Al-TM-Si (TM = Mn, Re) 1/1-cubic approximant
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Thermoelectric properties of the Al-TM-Si (TM = Mn, Re) 1/1-cubic approximant Tsunehiro Takeuchi1, Toshio Otagiri2, Hiroki Sakagami2, and Uichiro Mizutani2 Research Center for Advanced Waste and Emission Management, Nagoya University, Nagoya 464-8603, Japan 2 Department of Crystalline Materials Science, Nagoya University, Nagoya 464-8603, Japan 1
ABSTRACT The electrical resistivity, thermoelectric power, and thermal conductivity were investigated for the Al71.6-xMn 17.4Six and Al71.6-xRe 17.4Six (7 ≤ x ≤ 12) 1/1-cubic approximants. A large thermoelectric power ranging from -40 to 90 µV/K and a low thermal conductivity less than 3 W/K·cm were observed at room temperatures. The electrical resistivity at room temperature for these approximants was kept below 4,000 µΩcm, that is much smaller than that in the corresponding quasicrystals. As a result of the large thermoelectric power, the low thermal conductivity, and the low electrical resistivity, large dimensionless figure of merit ZT = 0.10 (n-type) and 0.07 (p-type) were achieved for the Al71.6Re17.4Si11 and Al71.6Mn17.4Si11 at room temperature, respectively.
INTRODUCTION Al-based Mackay-type Icosahedral quasicrystal is one of the potential candidates for a new thermoelectric material because of its possession of the large thermoelectric power (S) more than 50 µV/K [1] and low thermal conductivity (κ) as low as 1 W/K·m.[2] The large electrical resistivity (ρ) generally observed in the Al-based Mackay-type icosahedral quasicrystals, however, have prevented us to utilize the quasicrystals for a practical thermoelectric material. This large electrical resistivity cannot be eliminated because quasiperiodicity in the quasicystals strongly scatters the conduction electrons and the deep pseudogap across the Fermi level (EF) reduces the number of electrons contributing the electrical conduction. In order to overcome difficulty in reducing the electrical resistivity, we employed in this study the 1/1-cubic approximants rather than the highly resistive quasicrystals. Rational approximants including the 1/1-cubic approximants are known to possess a pseudogap across EF as well as their corresponding quasicrystals. If the large thermoelectric power of the quasicrystals is caused by the presence of pseudogap across EF, the large thermoelectric power should be also observed in the corresponding approximants. It is also important to note that the rational approximants have a periodic structure in which electrical conduction can be described with in the framework of Boltzmann transport theory. These approximants must possess much smaller electrical resistivity than that in the corresponding quasicrystals, provided that atoms in the approximants are aligned without any significant disordering. Although thermal conductivity in the approximants has not been deeply investigated yet, two conditions, relatively small electrical resistivity and large thermoelectric power, strongly encourage us to believe that these rational approximants possess a larger dimensionless figure of me
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