Scientists Hunt for New Energy Converting Alloys

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Thursday, July 4th, 2013
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Researchers from the California Institute of Technology and the University of Tokyo now say they have identified the best technique for determining the potential properties of different thermoelectric alloys.

Thermoelectric materials are capable of directly converting heat into electricity via complex interactions between the electrons in heavy metals such as antimony, lead or tellurium. They possess a number of distinct advantages compared to conventional forms of power generation due to the absence of discrete components, including reliability, lack of noise, and low maintenance requirements.

The materials are very expensive to build, however, and remain comparatively inefficient, with conversion percentages generally below 10 per cent. This has thus thus far limited their usage to niche areas such as powering space ships – an application first pioneered in the mid-20th century, and wine refrigeration.

The development of cheaper, more efficient thermoelectric alloys could have stunning implications for renewable energy, green building and other industries by reducing dependence on the carbon-based forms of power generation which lie at the crux of global climate change.

Scientists believe that they can dramatically lift the thermoelectric efficiency of the alloy materials via the right adjustments to their composition, crystal size and additives. The problem lies in the bewildering array of complex combinations available, which necessitates the use of theoretical calculations to assess their potential properties.

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In a study published on the open-access journal APL Materials, the research team from the California Institute of Technology and the University of Tokyo says a technique called “rigid band approximation” is capable of predicting a material’s properties with greater accuracy and ease than a more complex rival approach.

“The rigid band approach still supplies the simple, predictive engineering concepts we need for discovering fruitful thermoelectric material compositions,” says G. Jeffrey Snyder, the Caltech faculty associate in materials science who was responsible for leading the research.

While the rigid band approach provides only a relatively simple model of the electronic structure of a material, research by Snyder’s team has found that it is actually more accurate in predicting the properties of a material than the more complex “supercell” method, which provides a detailed depiction of ideal atomic arrangements.

“Supercell approaches are accurate for very specific dopant cases, but they do not take into account the various defects present in real materials,” Snyder said.

According to Snyder, the simpler technique will enable scientists to identify high efficiency thermoelectric alloys with far greater ease, which could have major implications for power generation in the near future.

A cheaper, more efficient thermoelectric alloy could convert the heat produced by engines and factories, which would otherwise be wasted, into free electricity. Snyder points to automobile engines as just one pertinent example of the alloy’s potential application.

“If we could double their efficiency, then thermoelectric modules incorporated into an automobile engine’s exhaust system could generate enough power to replace the alternator, which would increase the car’s gas mileage.”

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