Turning Up the Heat on Thermoelectrics

Estimated reading time: 6 minutes

In their theoretical modeling, the group calculated lead tin selenide’s ZT, or figure of merit, a quantity that tells you how close your material is to the theoretical limit for generating power from heat. The most efficient materials that have been reported so far have a ZT of about 2. Skinner and Fu found that, under a strong magnetic field of about 30 tesla, lead tin selenide can have a ZT of about 10 — five times more efficient than the best-performing thermoelectrics.

“It’s way off scale,” Skinner says. “When we first stumbled on this idea, it seemed a little too dramatic. It took a few days to convince myself that it all adds up.”

They calculate that a material with a ZT equal to 10, if heated at room temperature to about 500 kelvins, or 440 degrees Fahrenheit, under a 30-tesla magnetic field, should be able to turn 18 percent of that heat to electricity, compared to materials with a ZT equal to 2, which would only be able to convert 8 percent of that heat to energy.

The group acknowledges that, to achieve such high efficiencies, currently available topological semimetals would have to be heated under an extremely high magnetic field that could only be produced by a handful of facilities in the world. For these materials to be practical for use in power plants or automobiles, they should operate in the range of 1 to 2 tesla.

Fu says this should be doable if a topological semimetal were extremely clean, meaning that there are very few impurities in the material that would get in the way of electrons’ flow.

“To make materials very clean is very challenging, but people have dedicated a lot of effort to high-quality growth of these materials,” Fu says.

He adds that lead tin selenide, the material they focused on in their study, is not the cleanest topological semimetal that scientists have synthesized. In other words, there may be other, cleaner materials that may generate the same amount of thermal power with a much smaller magnetic field.

“We can see that this material is a good thermoelectric material, but there should be better ones,” Fu says. “One approach is to take the best [topological semimetal] we have now, and apply a magnetic field of 3 tesla. It may not increase efficiency by a factor of 2, but maybe 20 or 50 percent, which is already a pretty big advance.”

The team has filed a patent for their new thermolelectric approach and is collaborating with Princeton researchers to experimentally test the theory.

The research is supported by the Solid-State Solar Thermal Energy Conversion Center, an Energy Frontier Research Center of U.S. Department of Energy, and by Office of Basic Energy Sciences of U.S. Department of Energy.

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