Designing Nanocomposite Thermoelectric Materials

By Timothy D. Sands

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Thermoelectric effects are based on the difference between the average energy of the conduction electrons (or holes) and the Fermi energy. A thermoelectric material can be configured into a device for solid-state refrigeration or electrical power generation. Although these devices are presently restricted to niche applications - including beverage coolers, temperature control of communications lasers, and radioisotope thermoelectric generators for deep space probes –there is great potential for widespread application if the materials can be improved. In particular, an increase in the materials’ dimensionless figure-of-merit, ZT, from today’s values of ~1 to values above 4 would enable replacement of compressor based refrigeration with a solid-state alternative. Applications such as conversion of waste heat from vehicle exhaust to electric power would also become feasible. The key to designinghigh ZT materials is to manipulate phonons and electrons at the nanoscale. Confining electrons and holes can enhance the numerator of ZT, known as the power factor. Introducing defects that scatter phonons but not electrons can decrease the thermal conductivity (the denominator of ZT) without appreciably affecting the power factor.

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Tim Sands received his Ph.D. in Materials Science at the University of California, Berkeley in 1984. He joined the Purdue faculty in the fall of 2002 after nine years as a faculty member of the Department of Materials Science & Engineering at Berkeley. From 1984 to 1993, Sands was a Member of Technical Staff, a District Manager, and a research group Director at Bell Communications Research (Bellcore) in Red Bank, NJ. He has published over 200 papers and has been granted 11 patents in the areas of metal/semiconductor contacts, heteroepitaxy, thermoelectric materials, ferroelectric and piezoelectric materials and devices, semiconductor nanostructures, laser processing and heterogeneous integration. His present research efforts are directed toward the development of novel nanocomposite materials for applications in solid-state lighting, direct conversion of heat to electrical power, and thermoelectric refrigeration (see for more information). Professor Sands is presently the Basil S. Turner Professor of Engineering and a member of the Birck Nanotechnology Center, with joint appointments in the Schools of Materials Engineering and Electrical & Computer Engineering at Purdue.

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  • Timothy D. Sands (2005), "Designing Nanocomposite Thermoelectric Materials,"

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MSEE 239, Purdue University, West Lafayette, In