Riddle: What Metal Conducts Electricity, But Not Heat?

If you can’t answer the riddle, don’t feel bad. Metal conductors usually conduct electricity and heat. Usually, that’s true, but researchers at the Department of Energy’s Lawrence Berkeley National Laboratory and at the University of California, Berkeley, have found that vanadium dioxide can conduct electricity without conducting heat.

The Wiedemann-Franz Law states that good conductors of electricity are also good conductors of heat. Vanadium dioxide not only switches from an insulator to a conductor at 67C (152F), but it appears that it also doesn’t conduct as much heat as that law predicts while it is in its electrically conductive phase.

There are a few other materials that can conduct electricity better than heat, but these only operate at temperatures well below zero degrees. The researchers found that heat transfer attributable to random motion of electrons in a normal conductor is reduced in vanadium dioxide because the electrons move in a regular pattern like a moving fluid instead of randomly moving like particles.

By adding different materials to vanadium dioxide, the researchers were able to reduce the temperature that the material becomes a conductor as well as increase its ability to conduct heat. This allows tuning the material for specific uses.

In addition to providing new insights into how materials work, researchers hope the material will bring about advances in recovering waste heat and converting it to energy. This same team has been finding interesting uses for the exotic material, including using it as a micro robotic muscle (see video, below).

We’ve covered some of Berkeley’s exotic material antics before. We also check in on the national laboratories from time to time.

Photo credit: Junqiao Wu/Berkeley Lab

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