Rapid synthesis of high-performance thermoelectric materials directly from natural mineral tetrahedrite
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Rapid synthesis of high-performance thermoelectric materials directly from natural mineral tetrahedrite Xu Lu, Department of Physics and Astronomy, Michigan State University, East Lansing, Michigan 48824 Donald T. Morelli, Department of Physics and Astronomy, Michigan State University, East Lansing, Michigan 48824; Department of Chemical Engineering and Materials Science, Michigan State University, East Lansing, Michigan 48824 Address all correspondence to Donald T. Morelli at [email protected] (Received 14 May 2013; accepted 10 July 2013)
Abstract Tetrahedrite-structure compounds, of general composition Cu12−xZnxSb4S13, are an earth-abundant alternative to PbTe for thermoelectric power generation applications in the intermediate high-temperature range (300–400°C). Tetrahedrites can be synthesized in the laboratory using a multi-step process involving long annealing times. However, this compound also exists in natural mineral form, and, in fact, is one of the most abundant copper-bearing minerals in the world. We show here that by simply mixing natural mineral tetrahedrite with pure elements through high-energy ball milling without any further heat treatment, we can successfully obtain material with figure of merit near unity at 723 K.
Thermoelectric (TE) materials, which directly convert thermal energy into electricity through the Seebeck effect, have potential application in waste heat recovery and power generation. The overall performance of a TE material is determined by the dimensionless figure of merit:
zT =
a2 s T, k
where α is the Seebeck coefficient, σ the electrical conductivity, T the absolute temperature, and κ the thermal conductivity. Conventional established TE materials, such as Si-Ge alloys, Bi2Te3, and PbTe, have zT values of less than unity.[1] Recent progress in our understanding of the physics of thermoelectrics combined with advanced synthesis techniques have helped push zT values close to or even higher than two at high temperature. For example, one efficient way to increase zT is to control the structure of a material from the mesoscale to the nanoscale in order to scatter phonons with a wide range of wavelengths, resulting in low thermal conductivity without affecting the electronic transport properties.[2] Other approaches have sought to enhance the power factor (α2σ), for instance by implementing band structure engineering,[3] introducing resonant states,[4] or taking advantage of energy barrier filtering.[5] All of these methods typically require careful doping or nanostructuring, necessarily employing complex synthesis processes that involve significant energy, time, and human effort. This, together with the fact that many of the most high-performing TE materials are comprised of
expensive, toxic or rare elements, presents serious impediments to the large-scale application of TE materials. Another direct approach to increase zT is to design and synthesize TE materials with intrinsically low lattice thermal conductivity caused by large lattice anharmonicity.[6] One exam
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