Researchers at Berkeley Lab’s Materials Sciences Division have discovered a metal that conducts electricity, but not heat – a feature that contradicts the Wiedemann-Franz Law which states that good conductors of electricity will also be proportionally good conductors of heat.
This metal is known as Vanadium dioxide (VO2), dark blue inorganic compound which not only surprises us by its ability of not conducting heat but electricity, but it also has several other properties such as phase transition when close to room temperature. It can also change its electric conductivity and resistivity etc. in several orders and turn into an electrically conducting metal when at 67o C. It becomes transparent below 30o C and can absorb infrared light above 60o C.
Before the discovery of vanadium dioxide, researchers knew about a few metals which were good conductors of electricity but did not conduct heat better than they did with electricity. The temperature at which they exhibit such properties are very low i.e. hundreds of degrees below absolute zero, which is practically impossible.
But vanadium dioxide is the only metal found which not only is a good conductor of electricity but also it does not conduct heat even at the temperature above room temperature, which means that it is practically possible to use and extract several benefits out of its property.
Researcher Junqiao Wu, from Berkeley Lab’s Materials Sciences Division, said:
“This was a totally unexpected finding, 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 behaviour of novel conductors.”
After simulations and X-Rays, scientists at Berkeley Lab’s Materials Sciences Division at the University of California, Berkeley, found that electrons in vanadium dioxide can conduct electricity without conducting heat at the rate of thermal conductivity ten times smaller than which can be analyzed through Wiedemann-Franz Law.
According to Wu:
“The electrons were moving in unison with each other, much like a fluid, instead of as individual particles like in normal metals. For electrons, heat is a random motion. Normal metals transport heat efficiently because there are so many different possible microscopic configurations that the individual electrons can jump between.In contrast, the coordinated, marching-band-like motion of electrons in vanadium dioxide is detrimental to heat transfer as there are fewer configurations available for the electrons to hop randomly between.”
When researchers mixed the vanadium dioxide with other metals, they found that vanadium dioxide allows mixing up of its properties with some other elements, which can be very helpful in inventing such things never seen before.
Vanadium dioxide helps dissipate heat by conducting it at a certain temperature, which is lesser than an average insulator.
For example, when the researchers mixed up Vanadium dioxide with tungsten, they lowered the temperature so that the material can conduct heat and display its unique properties.
Fang Yang said about tuning vanadium dioxide with some other metal:
“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.”
Scientists are now trying to extract practical uses of vanadium dioxide to bring remarkable revolutions in the technology. For instance, conversion of heat from engines and other electronic appliances to electricity which will help to conserve power energy and save natural resources.
It can also be used to coat surfaces, such as sensors, in imaging and memory devices, along with building window coverings to keep the temperature of the buildings down. Confirmation about the properties are yet to be made, but surely some exciting times are coming ahead!
You can read more about the findings here.