Cost-effectiveness had been a key goal for researchers at Boston College and the Massachusetts Institute of Technology who announced in March that they have used nanotechnology to achieve a major increase in the thermoelectric efficiency of a bulk semiconductor alloy. The team’s low-cost approach,details of which are published in the online version of the journal Science, involves building tiny alloy nanostructures that can serve as micro-coolers and power generators. The researchers said that in addition to being inexpensive, their method will likely result in practical, near-term enhancements to make products consume less energy or capture energy that would otherwise be wasted.

The scientists were looking to recreate a common and lowcost material—bismuth antimony telluride—to conduct electricity but not heat. They achieved 40% of the semiconductor alloy’s
thermal conduction by crushing the alloy into nanoscopic dust and then reconstituting it in bulk form, albeit with nanoscale constituents . The grains and irregularities of the reconstituted alloy dramatically slowed the passage of phonons (a quantum mode of vibration) through the material, radically transforming the thermoelectric performance by blocking heat flow while allowing electrical flow.

The achievement marks the first such gain in a half-century 3.

Courtesy Boston College.jpg

Researchers produced a major increase in thermoelectric efficiency after using nanotechnology to restructure bismuth antimony telluride, a semiconductor alloy commonly used in industry and research. Viewed through a transmission electron microscope, colors highlight each nano-crystalline grain. Courtesy:Boston College, MIT, and GMZ Inc.

using a cost-effective material that functions at room temperatures and up to 482F. At its core, thermoelectricity is the “hot and cool” issue of physics. Heating one end of a wire, for example, causes electrons to move to the cooler end, producing an electric current.In reverse, applying a current to the same wire will carry heat away from a hot section to a cool section. Phonons play a key role because they are the primary means by which heat conduction takes place in insulating solids.Thermoelectric materials have been used by NASA to generate power for spacecraft.

These materials also have been used by specialty automobile seat makers to keep drivers cool during the summer. The auto industry has been experimenting with ways touse thermoelectric materials to convert waste heat from a car exhaust system into electric current to help power the vehicle. This research will be particularly influential in the development of solar energy technologies, as the conversion of solar heat into electricity is currently limited by materials that are less thermoelectrically efficient and more expensive.

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