18 May 2015 Inhomogeneous thermoelectric materials: improving overall zT by localized property variations
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Abstract
The search for improved thermoelectric materials is driven in part by the desire to convert otherwise wasted lowtemperature heat into useful electricity. In this work, we demonstrate a new path towards materials having higher overall zT, and consequently improved capacity to obtain more electrical power from a given content of heat. We produced alloys of (Bi,Sb)2Te3 using a special gas atomization process that is capable of producing source powder material having nanometer-scale grain size. When impulse-compacted by shockwave consolidation, the obtained dense solid will retain its nanostructure because insufficient time and temperature are available for the kinetics of any appreciable grain growth to proceed. However, if there is initial non-uniformity in the properties of the source powder, or if there is stress non-symmetries during shockwave consolidation, then the obtained consolidated material may have locally inhomogeneous properties distributed throughout the material. Thermoelectric property measurements from selected regions within the consolidated sample indicate a wide distribution of properties. For example, the thermal conductivity at room temperature ranged from as low as 1.30 Watts/m-K in one region to higher than 3.00 Watts/m-K in a neighboring region. The electrical resistivity showed similar variation from as low as 0.5 mΩ-cm to as high as 1.5 mΩ-cm. Individually, those regions exhibited thermoelectric material figure-of-merit, zT values ranging between 0.3 and 0.4. However, when combined into a dense nanocomposite, the overall ensemble zT approaches 0.7 which is nearly a factor of 2 higher.
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Narasimha Prasad, Narasimha Prasad, David Nemir, David Nemir, Jan Beck, Jan Beck, Jay Maddux, Jay Maddux, Patrick Taylor, Patrick Taylor, } "Inhomogeneous thermoelectric materials: improving overall zT by localized property variations", Proc. SPIE 9493, Energy Harvesting and Storage: Materials, Devices, and Applications VI, 949305 (18 May 2015); doi: 10.1117/12.2181143; https://doi.org/10.1117/12.2181143
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