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Ames Lab researchers boost thermoelectric conversion by TAGS materials

15 February 2011

A team led by researchers at the US Department of Energy’s Ames Laboratory recently reported that doping members of the well-established TAGS group—tellurium, antimony, germanium and silver—of thermoelectric materials with 1% of cerium or ytterbium can boost the thermoelectric figure of merit by up to 25%. The durable and relatively easy-to-produce material has numerous applications, including recycling waste heat from industrial refineries or using auto exhaust heat to help recharge the battery in an electric car.

The results of the group’s work appeared in a paper published online in November 2010 in the journal Advanced Functional Materials .

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 rare-earth elements modified the lattice, said Levin, referring to the crystal structure of the thermoelectric materials.

The group plans to test the material in order to better understand why the pronounced change took place and to boost its performance further.

Additionally, 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, the researchers said. 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.

Resources

  • E.M. Levin, B.A. Cook, J.L. Harringa, S. L. Bud’ko, R. Venkatasubramanian, K. Schmidt-Rohr (2010) Analysis of Ce- and Yb-Doped TAGS-85 Materials with Enhanced Thermoelectric Figure of Merit, Advanced Functional Materials, doi: 10.1002/adfm.201001307

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Comments

An increase of 25% on a 2% efficient converter would give a total efficiency of about 2.5%. Nothing to write home about.

HarveyD, I have to disagree. A relative improvement of 25% is significant. Even for the absolute improvement of 0.5%, it is all to do with context. If a PV manufacturer boosted their panel absolute conversion efficiency by 0.5% that would be news and the manufacture would no doubt have a big splashy press release to tout their new product.

The total efficiency (2.5%) of this form of low grade heat conversion also has to be put in context. If a car looses 60% of the fuel energy as heat and 2.5% of that is recovered, the overall efficiency of the car goes up by 1.5%. Big deal you say, but if the car is running at a fuel energy to mechanical energy efficiency of 15% then that is a 10% improvement in the useful energy. Not small beans.

There are already free piston Stirling machines with far greater efficiency. Sealed steam cycle generators would also work better and have been tested. ..HG..

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