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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 Ames Laboratory researchers found that adding just one percent of the rare-earth elements cerium or ytterbium to a TAGS material was sufficient to boost its performance. The team has yet to understand exactly why such a small compositional change in the material is able to profoundly affect its properties. However, they theorize that doping the TAGS material with either of the two rare-earth elements could affect several possible mechanisms that influence thermoelectric properties.
Team member Schmidt-Rohr studied the materials using Ames Laboratory’s solid-state nuclear magnetic resonance spectroscopy instruments. This enabled the researchers to verify that the one percent doping of cerium or ytterbium affected the structure of the thermoelectric material. In order to understand effect of magnetism of rare earths, team member Bud’ko studied magnetic properties of the materials.
The group plans to test the material in order to better understand why the pronounced change took place and, hopefully, to boost its performance further. The durable and relatively easy-to-produce material has innumerable applications, including recycling waste heat from industrial refineries or using auto exhaust heat to help recharge the battery in an electric car.
Additionally, the Ames Laboratory results, dependent as they were on doping TAGS with small amounts of cerium or ytterbium, provide more evidence of rare-earth elements’ strategic importance. Cerium or ytterbium are members of a group of 15 lanthanides, deemed essential to just about every new technology from consumer electronics and cell phones to hybrid car batteries and generator motors in wind turbines. Partial funding for this research was provided by the DARPA/DSO Program, along with the DOE Office of Science.