Progress on the Fabrication and Characterization of High Efficiency Thermoelectric Generators
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Progress on the Fabrication and Characterization of High Efficiency Thermoelectric Generators Timothy P. Hogan1, Adam D. Downey1, Jarrod Short1, Jonathan D’Angelo1, Eric Quarez2, John Androulakis2, Pierre F. P. Poudeu2, Mercouri G. Kanatzidis2, Ed Timm3, Kim Sarbo3, Harold Schock3 1 Department of Electrical and Computer Engineering, Michigan State University, East Lansing, MI 48824, U.S.A. 2Chemistry Department, Michigan State University, East Lansing, MI 48824, U.S.A. 3Department of Mechanical Engineering, Michigan State University, East Lansing, MI 48824, U.S.A. ABSTRACT High efficiency thermoelectric modules are of great interest for power generation applications where hot side temperatures of approximately 800K exist. The fabrication of such modules requires a multidisciplinary effort for the optimization of the material compositions, the engineering of the module systems, modeling and fabrication of the devices, and constant feedback from characterization. Pb-Sb-Ag-Te (LAST) and Pb-Sb-Ag-Sn-Te (LASTT) compounds are among the best known materials for this temperature range. Modeling of these materials and possible cascaded structures shows efficiencies of 14% can be achieved for low resistance contacts. Using antimony we have achieved contact resistivities less than 20 µΩ·cm2. Here we give a detailed presentation on the procedures used in the fabrication of thermoelectric generators based on these new materials. We also present the characterization systems and measurements on these generators. INTRODUCTION Various nanostructured materials are actively being investigated as possible high efficiency thermoelectric materials [1, 2, 3, 4]. The results have shown very low thermal conductivity materials can be fabricated, without significantly degrading the power factor. Several of these efforts are utilizing thin film techniques resulting in highly ordered samples with ZT’s as high as 3 at 550K [1]. Bulk samples in the AgPbmSbTe2+m and Ag(Pb1-xSnx)mSbTe2+m families of materials have been found to exhibit high figure of merits near 700K [5, 6, 7]. Through microscopy studies, endotaxial nanostructures were identified which are believed to result from a spinodal decomposition during the cooling phase of crystallization. Such nanostructures may be responsible for an enhanced phonon scattering without significant degradation of the power factor [8]. Further evaluations of these materials toward the fabrication of thermoelectric generators are reported in this manuscript. EXPERIMENTAL DETAILS We have developed a state of the art transport characterization laboratory at Michigan State University for the study of thermoelectric materials. The systems developed include a low temperature cryostat for the simultaneous measurements of electrical conductivity, thermoelectric power, and thermal conductivity from 77K to 400K, a system for the simultaneous measurements of electrical conductivity and thermoelectric power from 300K to 700K, and a tube furnace based measurement system for the simultaneous measurements of
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