Hybrid Composite Thermoelectric Materials Using Nanoscale Precursors
T.M. Tritt, J. He, B. Zhang, N. Gothard, X. Ji and J.W. Kolis
Clemson University, US
thermoelectrics, nanomaterials, energy harvesting
Recently new directions in bulk thermoelectric materials research have been pursued. The requirements for a potential thermoelectric material will be discussed and how these relate into giving a favorable figure of merit, ZT, defined as ZT = ?2T/??; where ? is the Seebeck coefficient, ? ______ electrical resistivity, ? __ ____ thermal conductivity and T is the temperature in Kelvin. Thermoelectric materials are inherently difficult to characterize and a short discussion of these difficulties will be part of the presentation. These difficulties are magnified at high temperatures and many challenges remain. Specific materials will be discussed, and especially those results in bulk materials that exhibit favorable properties for potential high temperature power generation capabilities. A brief discussion of the synthesis techniques, the characterization techniques and highlights of several systems of materials will be presented. Two-dimensional materials, such as TiS2, will also be discussed and why that this type of structure may well be critical to the development of the next generation thermoelectric materials. These two-dimensional layered compounds exhibit strong electron correlation within the layers, which may be the source of the high thermopower observed. Small grain sizes and their effect on thermal conductivity have been known for several years. This effect will be reviewed and used in relation to some of our recent results. A discussion of some of the future directions in our materials research will be highlighted, including some bulk materials, which are based on nano-scaled composites. PbTe is an intermediate temperature thermoelectric material, in the 450?C to 600?C range. PbTe nanocrystals, which are shown in Figure 1, have been grown in our labs by chemical vapor deposition. These materials grow in size selective regions exhibiting very high yield (100’s of mg) and have size distributions of around 100 nm to 1000 nm. In addition, Bi2Te3, another state of the art thermoelectric material and skutteruidites (CoSb3) have been synthesized as nanomaterials. These nano-materials will be incorporated into a bulk matrix, making a composite material in hopes of achieving a higher thermoelectric performance due to the increased phonon scattering that the nano-materials are expected to exhibit.
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Nanotech 2006 Conference Program Abstract