Doping Powers New Thermoelectric Material

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In the production of power, nearly two-thirds of energy input from fossil fuels is lost as waste heat. Industry is hungry for materials that can convert this heat to useful electricity, but a good thermoelectric material is hard to find.

Increasing the efficiency of thermoelectric materials is essential if they are to be used commercially. Northwestern University researchers now report that doping tin selenide with sodium boosts its performance as a thermoelectric material, pushing it toward usefulness. The doped material produces a significantly greater amount of electricity than the undoped material, given the same amount of heat input.

Details of the sodium-doped tin selenide -- the most efficient thermoelectric material to date at producing electricity from waste heat -- will be published Nov. 26 by the journal Science.

The Northwestern development could lead to new thermoelectric devices with potential applications in the automobile industry, glass- and brick-making factories, refineries, coal- and gas-fired power plants, and places where large combustion engines operate continuously (such as in large ships and tankers).

Most semiconducting materials, such as silicon, have only one conduction band to work with for doping, but tin selenide is unusual and has multiple bands; the researchers took advantage of these bands. They showed they could use sodium to access these channels and send electrons quickly through the material, driving up the heat conversion efficiency.

"The secret to our material is that multiband doping produces enhanced electrical properties," said Mercouri G. Kanatzidis, an inorganic chemist who led the multidisciplinary team. "By doping multiple bands, we are able to multiply the positive effect. To increase the efficiency, we need the electrons to be as mobile as possible. Tin selenide provides us with a superhighway -- it has at least four fast-moving lanes for hole carriers instead of one congested lane."

Kanatzidis, a Charles E. and Emma H. Morrison Professor of Chemistry in the Weinberg College of Arts and Sciences, is a world leader in thermoelectric materials research. He is a corresponding author of the paper.

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