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A1: Low temperature materials
One of the bottlenecks for widespread use of Thermoelectric (TE) generators as consumer products is toxicity of currently-used TE materials. In recent years, Si-based materials (e.g. nanostructured Si, MgSi2, and FeSi2) have been extensively studied as candidates of low-toxicity high-efficiency TE materials. On the other hands, the TE properties of Al-based materials have been scarcely studied, with a few exceptions such as YbAl3 and FeVAl2. Hence, we focused on Al6Ge5 as a candidate of novel Al-based TE material. Although there exist no intermetallic compounds in the Al-Ge binary phase diagram, it has been reported that a few intermetallic compounds such as Al6Ge5, Al3Ge2 exist as metastable phases. Among them, Al6Ge5 shows semiconductor properties with the crystal structure of rhombohedral (space group R-3c) which has a close relationship with that of the novel TE material Zn4Sb3. Thus, it is expected that Al6Ge5 shows a good TE performance, like Zn4Sb3. In the present study, we established a process to prepare single phase Al6Ge5 by a melt-spinning method with optimized various conditions, mainly the cooling rate. The metastable Al6Ge5 is stable below 473K, which was confirmed by the high temperature X-ray diffraction analysis. The TE properties of Al6Ge5 will be discussed.