New material provides greater thermoelectric conversion efficiency

Automobiles, military vehicles, even large-scale power generating facilities may someday operate far more efficiently thanks to a new alloy developed at the U.S. Department of Energy's Ames Laboratory. A team of researchers at the Lab that is jointly funded by the DOE Office of Basic Energy Sciences, Division of Materials Sciences and Engineering and the Defense Advanced Research Projects Agency, achieved a 25 percent improvement in the ability of a key material to convert heat into electrical energy.

''What happened here has not happened anywhere else,'' said Evgenii Levin, associate scientist at Ames Laboratory and co-principal investigator on the effort, speaking of the significant boost in efficiency documented by the research.  Along with Levin, the Ames Lab-based team included: Bruce Cook, scientist and co-principal investigator; Joel Harringa, assistant scientist II; Sergey Bud'ko, scientist; and Klaus Schmidt-Rohr, faculty scientist. Also taking part in the research was Rama Venkatasubramanian, who is director of the Center for Solid State Energetics at RTI International, located in North Carolina.

So-called thermoelectric materials that convert heat into electricity have been known since the early 1800s. One well-established group of thermoelectric materials is composed of tellurium, antimony, germanium and silver, and thus is known by the acronym ''TAGS.'' Thermoelectricity is based on the movement of charge carriers from their heated side to their cooler side, just as electrons travel along a wire.

The process, known as the Seebeck effect, was discovered in 1821 by Thomas Johann Seebeck, a physicist who lived in what is now Estonia. A related phenomenon observed in all thermoelectric materials is known as the Peltier effect, named after French physicist Jean-Charles Peltier, who discovered it in 1834. The Peltier effect can be utilized for solid-state heating or cooling with no moving parts.

In the nearly two centuries since the discovery of the Seebeck and Peltier effects, practical applications have been limited due to the low efficiency with which the materials performed either conversion. Significant work to improve that efficiency took place during the 1950s, when thermoelectric conversion was viewed as an ideal power source for deep-space probes, explained team member Cook. ''Thermoelectric conversion was successfully used to power the Voyager, Pioneer, Galileo, Cassini, and Viking spacecrafts,'' he said.

Despite its use by NASA, the low efficiency of thermoelectric conversion still kept it from being harnessed for more down-to-earth applications – even as research around the world continued in earnest. ''Occasionally, you would hear about a large increase in efficiency,'' Levin explained. But the claims did not hold up to closer scrutiny.