A material that is transparent at room temperature and can turn from insulator to conductor with a little bit of heat seems to be the stuff of science fiction, but it’s very real and it’s called metallic vanadium dioxide.
If these peculiarities weren’t enough, scientists have discovered another groundbreaking characteristic. As reported in Science, vanadium dioxide can conduct electricity much better than heat, which is a contradiction of the physical law that relates electrical and thermal conductivity in metals.
"This was a totally unexpected finding," principal investigator Junqiao Wu, a physicist at Berkeley Lab's Materials Sciences Division and a UC Berkeley professor of materials science and engineering, said in a statement. "It shows a drastic breakdown of a textbook law that has been known to be robust for conventional conductors. This discovery is of fundamental importance for understanding the basic electronic behavior of novel conductors."
Vanadium dioxide is 10 times more conductive of electricity than heat, and while is not the only material that can do this, they are usually found at temperatures hundreds of degrees below zero.
The secret of such a property is related to the limited number of configurations electrons can take in the material. In normal metals, electrons can move randomly (great for heat) and in specific directions (great for electricity).
In vanadium dioxide, electrons were observed moving together, like waves in a fluid, and not as discrete particles. This doesn’t stop directional movement, so electricity flows well, but it reduces the number of ways electrons can move chaotically, which means the material is a bad heat conductor.
This new property, combined with the fact that vanadium dioxide absorbs infrared light when it reaches a temperature of 60°C (140°F), makes the metal ideal for high-temperature applications.
"This material could be used to help stabilize temperature," added co-author Fan Yang, a postdoctoral researcher at Berkeley Lab's Molecular Foundry. "By tuning its thermal conductivity, the material can efficiently and automatically dissipate heat in the hot summer because it will have high thermal conductivity, but prevent heat loss in the cold winter because of its low thermal conductivity at lower temperatures."
Metallic vanadium dioxide is not ready to be commercialized just yet, but it’s definitely at the forefront of materials that might dramatically improve our tech.