Thermoelectric Materials: Principles, Structure, Properties, and Applications

During the 1990s there was a heightened interest in the field of thermoelectrics driven by the need for more efficient materials for electronic refrigeration and power generation (Nolas et al. 2002, Tritt et al. 2000a, Tritt et al. 1998, Tritt et al. 1997). Proposed industrial and military applications of thermoelectric (TE) materials are generating increased activity in this field by demanding higher performance, nearroom-temperature TE materials than those presently in use. Thermoelectric refrigeration is an environmentally ‘‘green’’ method of small-scale localized cooling in computers, infrared detectors, electronics, and opto-electronics as well as many other applications. However, most of the electronics and optoelectronics technologies typically require only small scale or localized spot cooling of small components which do not impose a large heat load. If significant economical cooling can be achieved the resulting ‘‘cold computing’’ could produce speed gains of 30– 200% in some CMOS computer processors. Cooling is perceived by many as the fundamental limit to electronic system performance. Cooling of laser diodes and infrared detectors to temperatures (T), between 100 K and 200 K, would greatly improve performance and sensitivity and thus is extremely important to many technologies. Thus, the potential payoff for the development of low-temperature thermoelectric refrigeration devices is great, and the requirement for compounds with properties optimized over wide temperature ranges has led to a much-expanded interest in new thermoelectric materials. Utilization of Peltier coolers in relation to refrigeration of biological specimens/samples is an emerging application of thermoelectrics. Power generation applications are being investigated by the automotive industry as a means to develop electrical power from waste engine heat for use in the ‘‘next generation vehicle.’’ These uses range from power generation utilizing waste engine heat from the exhaust and radiator cooling system to seat coolers for comfort or electronic component cooling. Of course, the deep space applications of NASA’s Voyager and Cassini missions using radioactive thermoelectric generators (RTGs) are well established. Given the present energy needs experienced in the United States there is even a more pressing need to investigate alternative energy conversion technologies in this country, e.g., the thermal to electrical energy conversion from natural heat gradients that thermoelectric technologies provide. This has already been identified as important in many European and Asian countries. An overview of the state-of-the-art materials, a theoretical and experimental discussion of the basic principles, as well as an overview of some of the recent developments and materials is given in the texts of Tritt and Nolas (Nolas et al. 2001a, Tritt 2000a).