annurev.matsci.29.1 - P1 SAT/ARY P2 PKS/PLB QC PKS/anil T1...

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Annu. Rev. Mater. Sci. 1999. 29:89–116 Copyright c ± 1999 by Annual Reviews. All rights reserved SKUTTERUDITES: A Phonon-Glass-Electron Crystal Approach to Advanced Thermoelectric Energy Conversion Applications G. S. Nolas Research and Development Division, Marlow Industries Inc., Dallas, Texas 75238 D. T. Morelli General Motors Research and Development Center, Warren, Michigan 48090 Terry M. Tritt Department of Physics and Astronomy, Kinard Laboratory, Clemson University, Clemson, South Carolina 29634 KEY WORDS: electronic refrigeration, thermopower, semiconductors ABSTRACT Recently there has been a resurgence of research efforts related to the investi- gation of new and novel materials for small-scale thermoelectric refrigeration and power generation applications. These materials need to couple and opti- mize a variety of properties in order to exhibit the necessary figure of merit, i.e. the numerical expression that is commonly used to compare one poten- tial thermoelectric material with another. The figure of merit is related to the coefficient of performance or efficiency of a particular device made from a mate- rial. The best thermoelectric material should possess thermal properties similar to that of a glass and electrical properties similar to that of a perfect single- crystal material, i.e. a poor thermal conductor and a good electrical conduc- tor. Skutterudites are materials that appear to have the potential to fulfill such criteria. These materials exhibit many types of interesting properties. For exam- ple, skutterudites are members of a family of compounds we call open structure or cage-like, materials. When atoms are placed into the interstitial voids or cages of these materials, the lattice thermal conductivity can be substantially reduced 89 0084-6600/99/0801-0089$08.00 Annu. Rev. Mater. Sci. 1999.29:89-116. Downloaded from by California Institute of Technology on 02/24/10. For personal use only.
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90 NOLAS, MORELLI & TRITT compared with that of unfilled skutterudites. These compounds exhibit electrical properties ranging from that of low-temperature superconductors to narrow gap semiconductors. INTRODUCTION TO THERMOELECTRIC PHENOMENA AND APPLICATIONS Background A discussion of thermoelectric effects should start with the most fundamental thermoelectric phenomenon, the Seebeck effect. In the early 1800s, Seebeck observed that if two dissimilar materials are joined together and the junctions are held at different temperatures (T and T + 1 T) a voltage difference ( 1 V) is developed that is proportional to the temperature difference. The ratio of the voltage developed to the temperature gradient ( 1 V/ 1 T) is related to an intrin- sic property of the materials called the Seebeck coefficient ( α ) or thermopower. The Seebeck coefficient is very low for metals (of the order of 1 to 10 μ V/K) and much larger for semiconductors (10 2 to 10 3 μ V/K). A related effect was discovered a few years later by Peltier, who observed that if a current is passed through the junction of two dissimilar materials, heat is reversibly absorbed or rejected at the junction depending on the current direction. This phenomenon,
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This note was uploaded on 05/21/2010 for the course MS Thermoelec taught by Professor Snyder during the Spring '10 term at Caltech.

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annurev.matsci.29.1 - P1 SAT/ARY P2 PKS/PLB QC PKS/anil T1...

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