Convergence of electronic bands for high performance bulk thermoelectrics

• Published in: Nature (London) Vol. 473; no. 7345; pp. 66 - 69
• Main Authors: Pei, Yanzhong, Shi, Xiaoya, LaLonde, Aaron, Wang, Heng, Chen, Lidong, Snyder, G. Jeffrey
• Format: Journal Article
• Language: English
• Published: London Nature Publishing Group UK 05.05.2011; Nature Publishing Group
• Subjects: 639/166; 639/301/299/2736; Bands; Condensed matter: electronic structure, electrical, magnetic, and optical properties; Conductivity phenomena in semiconductors and insulators; Convergence; Electricity; Electronic transport in condensed matter; Electronics; Exact sciences and technology; Heat recovery; Humanities and Social Sciences; letter; multidisciplinary; Nanostructure; Physics; Product development; Properties; Science; Science (multidisciplinary); Searching; Solid solutions; Standard deviation; Studies; Symmetry; Thermal conductivity; Thermoelectric and thermomagnetic effects; Thermoelectric generators; Thermoelectric materials; Thermoelectricity; Valleys; Vehicle emissions; Waste recovery; United States; Doping; Seebeck effect; Lead Selenides tellurides; Lattice parameters; Sodium additions; Thermoelectric materials; Impurities; Thermoelectric power; Degenerate semiconductor; Chemical composition; Carrier density; Lattice thermal conductivity; Distribution functions
• ISSN: 0028-0836; 1476-4687
• DOI: 10.1038/nature09996

Hot source The use of thermoelectric devices to convert waste heat into electricity is anticipated to find many applications, but most thermoelectric materials are relatively inefficient. Attempts are being made to improve this situation, with many researchers focusing on the use of nanostructuring to engineer the desired combination of thermal and electrical properties into the devices. Pei and colleagues now show that such a tailoring of properties is also possible in a bulk alloy through careful control of composition and chemical doping, yielding a high performance thermoelectric material. Thermoelectric generators, which directly convert heat into electricity, have long been relegated to use in space-based or other niche applications, but are now being actively considered for a variety of practical waste heat recovery systems—such as the conversion of car exhaust heat into electricity. Although these devices can be very reliable and compact, the thermoelectric materials themselves are relatively inefficient: to facilitate widespread application, it will be desirable to identify or develop materials that have an intensive thermoelectric materials figure of merit, zT , above 1.5 (ref. 1 ). Many different concepts have been used in the search for new materials with high thermoelectric efficiency, such as the use of nanostructuring to reduce phonon thermal conductivity 2 , 3 , 4 , which has led to the investigation of a variety of complex material systems 5 . In this vein, it is well known 6 , 7 that a high valley degeneracy (typically ≤6 for known thermoelectrics) in the electronic bands is conducive to high zT , and this in turn has stimulated attempts to engineer such degeneracy by adopting low-dimensional nanostructures 8 , 9 , 10 . Here we demonstrate that it is possible to direct the convergence of many valleys in a bulk material by tuning the doping and composition. By this route, we achieve a convergence of at least 12 valleys in doped PbTe 1 −  x Se x alloys, leading to an extraordinary zT value of 1.8 at about 850 kelvin. Band engineering to converge the valence (or conduction) bands to achieve high valley degeneracy should be a general strategy in the search for and improvement of bulk thermoelectric materials, because it simultaneously leads to a high Seebeck coefficient and high electrical conductivity.