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Unformatted text preview: nature materials | VOL 7 | FEBRUARY 2008 | www.nature.com/naturematerials 105 REVIEW ARTICLE G. JEFFREY SNYDER* AND ERIC S. TOBERER Materials Science, California Institute of Technology, 1200 East California Boulevard, Pasadena, California 91125, USA *e-mail: email@example.com The worlds demand for energy is causing a dramatic escalation of social and political unrest. Likewise, the environmental impact of global climate change due to the combustion of fossil fuels is becoming increasingly alarming. One way to improve the sustainability of our electricity base is through the scavenging of waste heat with thermoelectric generators (Box 1). Home heating, automotive exhaust, and industrial processes all generate an enormous amount of unused waste heat that could be converted to electricity by using thermoelectrics. As thermoelectric generators are solid-state devices with no moving parts, they are silent, reliable and scalable, making them ideal for small, distributed power generation 1 . Efforts are already underway to replace the alternator in cars with a thermoelectric generator mounted on the exhaust stream, thereby improving fuel efficiency 2 . Advances in thermoelectrics could similarly enable the replacement of compression-based refrigeration with solid-state Peltier coolers 3 . Thermoelectrics have long been too inefficient to be cost- effective in most applications 4 . However, a resurgence of interest in thermoelectrics began in the mid 1990s when theoretical predictions suggested that thermoelectric efficiency could be greatly enhanced through nanostructural engineering, which led to experimental efforts to demonstrate the proof-of-principle and high-efficiency materials 5,6 . At the same time, complex bulk materials (such as skutterudites 7 , clathrates 8 and Zintl phases 9 ) have been explored and found that high efficiencies could indeed be obtained. Here, we review these recent advances, looking at how disorder and complexity within the unit cell as well as nanostructured materials can lead to enhanced efficiency. This survey allows us to find common traits in these materials, and distill rational design strategies for the discovery of materials with high thermoelectric efficiency. More comprehensive reviews on thermoelectric materials are well covered in several books 1,1012 and articles 3,5,6,8,1318 . CONFLICTING THERMOELECTRIC MATERIAL PROPERTIES Fundamental to the field of thermoelectric materials is the need to optimize a variety of conflicting properties. To maximize the thermoelectric figure of merit ( zT ) of a material, a large thermopower (absolute value of the Seebeck coefficient), high electrical conductivity, and low thermal conductivity are required. As these transport characteristics depend on interrelated material properties, a number of parameters need to be optimized to maximize zT ....
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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.
- Spring '10