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Power from heat

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11:25am, March 26, 2008

The thermoelectric effect can produce small amounts of electricity from almost any source of heat, but its low efficiency has so far limited its uses. A team has now found a simple way to make one thermoelectric alloy more efficient.

When two ends of a stick of a thermoelectric material are exposed to different temperatures, a voltage appears. The electrons in the stick act like the molecules in a gas: Just as gas expands when heated, the heated electrons move from the hotter side to the cooler side. The resulting voltage can create current.

Since the 1950s, researchers have known that the alloy bismuth antimony telluride is a good thermoelectric material, says Gang Chen of the Massachusetts Institute of Technology. But Chen wondered if the effect could be made better. Chen and his colleagues ground up the alloy and recompressed it. The grinding reduced the size of the alloy's crystalline grains by about a factor of a thousand. This change slightly improved the material

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