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, Ames, Iowa. 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
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.
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.
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.
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.
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.
that changed in 2010, when 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.
results of the group’s work appeared in the article, “Analysis of Ce-
and Yb-Doped TAGS-85 Materials with Enhanced Thermoelectric Figure of
Merit,” published online in November 2010 in the journal Advanced
Functional Materials (see below).
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.
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. “Rare-earth
elements modified the lattice,” said Levin, referring to the crystal
structure of the thermoelectric materials.
group plans to test the material in order to better understand why the
pronounced change took place and, hopefully, to boost its performance
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. “It’s a very amazing area,” Levin said, particularly since many
years of prior research into TAGS materials enables researchers to
understand their nature. Better understanding of the thermoelectric and
their improvement can immediately result in applications at larger
scale than now.
the Ames Laboratory results – dependent as they were on doping TAGS
with small amounts of cerium or ytterbium – provide yet 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. The Ames
Laboratory has been a leader in rare-earth research going back to the
closing days of World War II. Fears of shortages of rare-earth elements
have caused these little-known materials to be a much-talked-about
subject in the news lately.
more information, see: E.M. Levin, B.A. Cook, J.L. Harringa, S. L.
Bud’ko, R. Venkatasubramanian, K. Schmidt-Rohr, “Analysis of Ce- and
Yb-Doped TAGS-85 Materials with Enhanced Thermoelectric Figure of
Merit,” Advanced Functional Materials, 2010, in press. DOI:
Partial funding for this research was provided by the DARPA/DSO Program, along with the DOE Office of Science.