Artificially nanostructured n-type SiGe bulk thermoelectrics through plasma enhanced growth of alloy nanoparticles from the gas phase

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SiGe alloys belong to the class of classic high temperature thermoelectric materials. By the means of nanostructuring, the performance of this well-known material can be further enhanced. Additional grain boundaries and point defects added to the alloy structure result in a strong decrease in thermal conductivity because of reduced lattice contribution to the overall thermal conductivity. Hence, the figure of merit can be increased. To obtain a nanostructured bulk material, a nanosized raw material is essential. In this work, a new approach toward nanostructured SiGe alloys is presented where alloyed nanoparticles are synthesized from a homogeneous mixture of the respective precursors in a microwave plasma reactor. As-prepared nanoparticles are compacted to a dense bulk material by a field assisted sintering technique. A figure of merit of zT = 0.5 ± 0.09 at 450 °C and a peak zT of 0.8 ± 0.15 at 1000 °C could be achieved for a nanostructured, 0.8% phosphorus-doped Si80Ge20 alloy without any further optimization.

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We thank M. Winterer and D. Gautam, Faculty of Engineering, for the use of the spark plasma sintering machine and M. Farle, Department of Experimental Physics, for the possibility to use the microscopy facilities. Financial supports from the German Research Foundation (Deutsche Forschungsgemeinschaft) within the priority program SPP 1386: Nanostrukturierte Thermoelektrika, the European Union and the Ministry of Economic Affairs and Energy of the State North Rhine–Westphalia in Germany within the frame of an Objective 2 Programme (European Regional Development Fund) are gratefully acknowledged.

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Stein, N., Petermann, N., Theissmann, R. et al. Artificially nanostructured n-type SiGe bulk thermoelectrics through plasma enhanced growth of alloy nanoparticles from the gas phase. Journal of Materials Research 26, 1872–1878 (2011).

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