Bulk Materials Research for Thermoelectric Power Generation Applications
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1044-U05-01
Bulk Materials Research for Thermoelectric Power Generation Applications George Nolas, Matthew Beekman, Joshua Martin, Dongli Wang, and Xiunu sophie Lin University of South Florida, Tampa, FL, 33620 ABSTRACT There are a variety of material systems employing different strategies in an effort to establish a new paradigm for thermoelectric materials performance. One approach is the PGEC, or “phonon-glass electron crystal”, approach were research towards optimization of the electrical properties of very low thermal conductivity materials is key. Other efforts focus on materials that exhibit high power factors via quantum-confinement or nano-scale affects. Still others focus on “engineering” metastable phases that possess properties that are distinct, if not unique, to solid state chemistry. All these approaches are valid and provide a fundamental knowledge base whereby present and future scientific materials discoveries will lead to new technological improvements. This paper focuses on bulk materials, in particular those material systems currently under investigation in the novel materials laboratory at the University of South Florida and the requirements and strategies for their optimization towards improved thermoelectric properties. INTRODUCTION The demand for new technologies to enhance the efficiency of energy production is at the forefront of new materials research towards power conversion technologies. Thermoelectric (TE) power conversion from “waste” heat is a viable technology that can be instrumental in improving this efficiency. TE technology is advantageous in many respects, including reliability (no moving parts), safety, and environmental friendliness. The specific material property requirements can be quantified by the dimensionless figure of merit, ZT = S2/ρκ where S is the Seebeck coefficient, ρ the electrical resistivity and κ the total thermal conductivity (κ = κL + κe; the lattice and electronic contributions, respectively). The power factor, S2/ρ, is typically optimized as a function of carrier concentration (typically ~ 1019 carriers/cm3 in materials presently available in devices), through doping, to give the largest ZT.
The current TE materials used in devices are rather inefficient, ZT ≈ 1, even though they are able to address many niche applications. In order that TE devices achieve their full potential, new materials and new material synthesis approaches are needed. Very recently research on TE materials has resulted in ZT values greater than unity at different temperatures of application. This achievement is due to the advanced materials synthesis, characterization, and modeling capabilities developed over the past ten years, as well as the identification of new classes of materials that show enhanced thermoelectric properties. Several classes of materials have contributed to these advances. These include bulk materials such as skutterudites and clathrates [1-6], and complex chalcogenides [7] with unique crystal structures allowing for low κL and therefore enhanced thermoelectr
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