Nanotechnology Now

Our NanoNews Digest Sponsors

Heifer International

Wikipedia Affiliate Button

Home > Press > Mismatched alloys are a good match for thermoelectrics

Contour plots showing electronic density of states in HMAs created from zinc selenide by the addition of (a) 3.125-percent oxygen atoms, and (b) 6.25 percent oxygen. The zinc and selenium atoms are shown in light blue and orange. Oxygen atoms (dark blue) are surrounded by high electronic density regions. (Image provided by Junqiao Wu)
Contour plots showing electronic density of states in HMAs created from zinc selenide by the addition of (a) 3.125-percent oxygen atoms, and (b) 6.25 percent oxygen. The zinc and selenium atoms are shown in light blue and orange. Oxygen atoms (dark blue) are surrounded by high electronic density regions. (Image provided by Junqiao Wu)

Abstract:
Employing some of the world's most powerful supercomputers, scientists at Lawrence Berkeley National Laboratory have shown that mismatched alloys are a good match for the future development of high performance thermoelectric devices. Thermoelectrics hold enormous potential for green energy production because of their ability to convert heat into electricity.

Mismatched alloys are a good match for thermoelectrics

Berkeley, CA | Posted on January 29th, 2010

Computations performed on "Franklin," a Cray XT4 massively parallel processing system operated by the National Energy Research Scientific Computing Center (NERSC), showed that the introduction of oxygen impurities into a unique class of semiconductors known as highly mismatched alloys (HMAs) can substantially enhance the thermoelectric performance of these materials without the customary degradation in electric conductivity.

"We are predicting a range of inexpensive, abundant, non-toxic materials in which the band structure can be widely tuned for maximal thermoelectric efficiency," says Junqiao Wu, a physicist with Berkeley Lab's Materials Sciences Division and a professor with UC Berkeley's Department of Materials Science and Engineering who led this research.

"Specifically, we've shown that the hybridization of electronic wave functions of alloy constituents in HMAs makes it possible to enhance thermopower without much reduction of electric conductivity, which is not the case for conventional thermoelectric materials," he says.

Collaborating with Wu on this work were Joo-Hyoung Lee and Jeffrey Grossman, both now at the Massachusetts Institute of Technology. The team published a paper on these results in Physical Review Letters titled, "Enhancing the Thermoelectric Power Factor with Highly Mismatched Isoelectronic Doping."

Seebeck Effect and Green Energy

In 1821, the German-Estonian physicist Thomas Johann Seebeck observed that a temperature difference between two ends of a metal bar created an electrical current in between, with the voltage being directly proportional to the temperature difference. This phenomenon became known as the Seebeck thermoelectric effect and it holds great promise for capturing and converting into electricity some of the vast amounts of heat now being lost in the turbine-driven production of electrical power. For this lost heat to be reclaimed, however, thermoelectric efficiency must be significantly improved.

"Good thermoelectric materials should have high thermopower, high electric conductivity, and low thermal conductivity," says Wu. "Enhancement in thermoelectric performance can be achieved by reducing thermal conductivity through nanostructuring. However, increasing performance by increasing thermopower has proven difficult because an increase in thermopower has typically come at the cost of a decrease in electric conductivity."

To get around this conundrum, Wu and his colleagues turned to HMAs, an unusual new class of materials whose development has been led by another physicist with Berkeley Lab's Materials Sciences Division, Wladyslaw Walukiewicz. HMAs are formed from alloys that are highly mismatched in terms of electronegativity, which is a measurement of their ability to attract electrons. The partial replacement of anions with highly electronegative isoelectronic ions makes it possible to fabricate HMAs whose properties can be dramatically altered with only a small amount of doping. Anions are negatively charged atoms and isoelectronic ions are different elements that have identical electronic configurations.

"In HMAs, the hybridization between extended states of the majority component and localized states of the minority component results in a strong band restructuring, leading to peaks in the electronic density of states and new sub bands in the original band structure," Wu says. "Owing to the extended states hybridized into these sub bands, high electric conductivity is largely maintained in spite of alloy scattering."

In their theoretical work, Wu and his colleagues discovered that this type of electronic structure engineering can be greatly beneficial for thermoelectricity. Working with the semiconductor zinc selenide, they simulated the introduction of two dilute concentrations of oxygen atoms (3.125 and 6.25 percent respectively) to create model HMAs. In both cases, the oxygen impurities were shown to induce peaks in the electronic density of states above the conduction band minimum. It was also shown that charge densities near the density of state peaks were substantially attracted toward the highly electronegative oxygen atoms.

Wu and his colleagues found that for each of the simulation scenarios, the impurity-induced peaks in the electronic density of states resulted in a "sharp increase" of both thermopower and electric conductivity compared to oxygen-free zinc selenide. The increases were by factors of 30 and 180 respectively.

"Furthermore, this effect is found to be absent when the impurity electronegativity matches the host that it substitutes," Wu says. "These results suggest that highly electronegativity-mismatched alloys can be designed for high performance thermoelectric applications."

Wu and his research group are now working to actually synthesize HMAs for physical testing in the laboratory. In addition to capturing energy that is now being wasted, Wu believes that HMA-based thermoelectrics can also be used for solid state cooling, in which a thermoelectric device is used to cool other devices or materials.

"Thermoelectric coolers have advantages over conventional refrigeration technology in that they have no moving parts, need little maintenance, and work at a much smaller spatial scale," Wu says.

This project was supported under Berkeley Lab's Laboratory Directed Research and Development Program.

Additional Information

For more information on the research of Junqiao Wu, visit his Website at www.mse.berkeley.edu/~jwu/

The paper "Enhancing the Thermoelectric Power Factor with Highly Mismatched Isoelectronic Doping" can be viewed on the Website of Physical Review Letters at www2.me.berkeley.edu/~jwu/publications/Lee-PRL-10.pdf

####

About Berkeley Lab
Berkeley Lab is a U.S. Department of Energy national laboratory located in Berkeley, California. It conducts unclassified scientific research for DOE’s Office of Science and is managed by the University of California.

For more information, please click here

Contacts:
Lynn Yarris
(510) 486-5375

Copyright © Berkeley Lab

If you have a comment, please Contact us.

Issuers of news releases, not 7th Wave, Inc. or Nanotechnology Now, are solely responsible for the accuracy of the content.

Bookmark:
Delicious Digg Newsvine Google Yahoo Reddit Magnoliacom Furl Facebook

Related News Press

News and information

Novel nanoparticle-based approach detects and treats oral plaque without drugs August 17th, 2018

UVA multidisciplinary engineering team designs technology for smart materials: The invention could lead to devices and manufactured goods, such as fabrics, that can dynamically regulate between thermally insulating and cooling August 17th, 2018

Smallest transistor worldwide switches current with a single atom in solid electrolyte: Milestone of energy efficiency in information technology -- Publication in Advanced Materials August 17th, 2018

Scientists turn to the quantum realm to improve energy transportation August 17th, 2018

Govt.-Legislation/Regulation/Funding/Policy

UVA multidisciplinary engineering team designs technology for smart materials: The invention could lead to devices and manufactured goods, such as fabrics, that can dynamically regulate between thermally insulating and cooling August 17th, 2018

Scientists turn to the quantum realm to improve energy transportation August 17th, 2018

Research brief: UMN researchers use green gold to rapidly detect and identify harmful bacteria August 15th, 2018

Particles pull last drops of oil from well water: Rice University engineers find nanoscale solution to 'produced water' problem August 15th, 2018

Possible Futures

Novel nanoparticle-based approach detects and treats oral plaque without drugs August 17th, 2018

UVA multidisciplinary engineering team designs technology for smart materials: The invention could lead to devices and manufactured goods, such as fabrics, that can dynamically regulate between thermally insulating and cooling August 17th, 2018

Smallest transistor worldwide switches current with a single atom in solid electrolyte: Milestone of energy efficiency in information technology -- Publication in Advanced Materials August 17th, 2018

Scientists turn to the quantum realm to improve energy transportation August 17th, 2018

Announcements

Novel nanoparticle-based approach detects and treats oral plaque without drugs August 17th, 2018

UVA multidisciplinary engineering team designs technology for smart materials: The invention could lead to devices and manufactured goods, such as fabrics, that can dynamically regulate between thermally insulating and cooling August 17th, 2018

Smallest transistor worldwide switches current with a single atom in solid electrolyte: Milestone of energy efficiency in information technology -- Publication in Advanced Materials August 17th, 2018

Scientists turn to the quantum realm to improve energy transportation August 17th, 2018

Environment

Particles pull last drops of oil from well water: Rice University engineers find nanoscale solution to 'produced water' problem August 15th, 2018

FEFU scientists reported on toxicity of carbon and silicon nanotubes and carbon nanofibers: Nanoparticles with a wide range of applying, including medicine, damage cells of microalgae Heterosigma akashivo badly. July 18th, 2018

Nanomaterials could mean more algae outbreaks for wetlands, waterways: High tech metal particles may inadvertently take a toll on aquatic life June 26th, 2018

Squeezing light at the nanoscale: Ultra-confined light could detect harmful molecules June 17th, 2018

Energy

Smallest transistor worldwide switches current with a single atom in solid electrolyte: Milestone of energy efficiency in information technology -- Publication in Advanced Materials August 17th, 2018

Scientists turn to the quantum realm to improve energy transportation August 17th, 2018

Particles pull last drops of oil from well water: Rice University engineers find nanoscale solution to 'produced water' problem August 15th, 2018

CTI Materials drives nano commercialization with it's patented surfactant free nanoparticle dispersions August 15th, 2018

NanoNews-Digest
The latest news from around the world, FREE



  Premium Products
NanoNews-Custom
Only the news you want to read!
 Learn More
NanoStrategies
Full-service, expert consulting
 Learn More











ASP
Nanotechnology Now Featured Books




NNN

The Hunger Project