February 2013

Making the Right Substitution for Better Thermoelectrics

Exploiting the self-organizing nature of atoms to block heat transfer and improve thermal-to-electrical energy conversion.

Click to enlarge photo. Enlarge Photo

Image courtesy of Ctirad Uher

Crystal structure of CoSb3(1-x)Ge1.5xTe1.5x, where Ge(germanium) and Te (tellurium) atoms are substituted for Sb (antimony) atoms.  In the unit cell shown, the Sb atoms (or their substitutes) are arranged in octahedra (blue) with a single Co (cobalt) atom inside (not visible).

The Science

Research predicted and experimentally verified that creating local atomic disorder in thermoelectric materials by substituting atoms into specific atomic sites (i.e., doping) would disrupt the atomic vibrations that govern heat transport and would result in a low thermal conductivity for the doped material.

The Impact

Unwanted heat transfer in thermoelectric materials limits the efficiency of thermal-to-electrical energy conversion devices. Thus, reducing the thermal conductivity increases the efficiency of the devices and opens economical ways to collect waste heat in cars, trucks, and industrial processes and directly convert it to electricity.

Summary

Like a coach in sports, making the right substitution can make the difference between winning and losing. Using a combination of theory and simulations, the researchers at the University of Michigan EFRC predicted that replacing some of the antimony (Sb) atoms in the skutterudite mineral, cobalt antimonide (CoSb3), would disrupt the atomic vibrations that play a crucial role in transferring heat through the material – but only if the replacement atoms took up specific atomic locations in the crystal structure. Quantum mechanical calculations were used to predict that entire 4-member rings of Sb atoms (Sb4) would be replaced by cross-diagonal rings of Ge2Te2 due to the natural, atomic ordering tendencies of alloying elements. The consequences of this substitution order on the atomic vibrations responsible for heat transfer was verified by molecular dynamic simulations and then experimentally demonstrated by measuring the reduction in the thermal conductivity for the substituted material CoSb3(1-x)Ge1.5xTe1.5x. This approach and resulting insights can be extended to other families of thermoelectric materials to reduce the thermal conductivity of these materials and increase the efficiency of heat-to-electricity conversion for thermoelectric devices.

Contact

Ctirad Uher
University of Michigan
cuher@umich.edu

Peter Green
Director, Center for Solar and Thermal Energy Conversion (CSTEC) EFRC
pfgreen@umich.edu

Funding

DOE Office of Science, Basic Energy Sciences, Energy Frontier Research Centers (EFRC) Program. Materials synthesis was supported by the Natural Science Foundation of China and the International Science & Technology Cooperation Program of China.

Publications

H. Chi, H. Kim, J. C. Thomas, X. Su, S. Stackhouse, M. Kaviany, A. Van der Ven, X. Tang, and C. Uher, “Configuring pnicogen rings in skutterudites for low phonon conductivity.” Phys. Rev. B 86, 195209 (2012);   [DOI: 10.1103/PhysRevB.86.195209External link].

H. Kim, M. Kaviany, J. C. Thomas, A. Van der Ven, C. Uher, and B. Huang, “Structural Order-Disorder Transitions and Phonon Conductivity of Partially Filled Skutterudites” Phys. Rev. Lett. 105, 265901 (2010);  [DOI: 10.1103/PhysRevLett.105.265901External link]

Related Links

University of Michigan Press ReleaseExternal link

Center for Solar and Thermal Energy Conversion (CSTEC) EFRC 

CSTEC HomepageExternal link

Highlight Categories

Program: BES, EFRCs

Performer/Facility: University

Additional: Collaborations, International Collaboration

Last modified: 12/5/2013 5:18:06 PM