Scientists Discover Metal That Conducts Electricity But Not Heat

UPI ^ | Jan. 26, 2017 | Brooks Hays

[nickcarraway]

"This material could be used to help stabilize temperature," said researcher Fan Yang.

Researchers have discovered a metal that fails to comply with the Wiedemann-Franz Law, the rule that suggests good conductors of electricity will also be good conductors of thermal energy.

Metallic vanadium dioxide easily carries an electric current, but fails to conduct heat as expected.

"This was a totally unexpected finding," Junqiao Wu, a professor of materials science and engineering at the University of California, Berkeley, said in a news release. "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."

The revelation -- detailed in the journal Science -- furthers the oddball reputation of metallic vanadium dioxide.

Previous studies showed the substance is an insulator at room temperature, but becomes a conductor once it reachers a temperature of 152 degrees Fahrenheit.

Researchers used electron scanning imagery to observe the movement of heat energy across the material. Modeling and lab experiments helped scientists determine how much heat was being carried by electrons and how much was being propagated by the vibration of the material's unique crystal lattices, or phonons.

"The electrons were moving in unison with each other, much like a fluid, instead of as individual particles like in normal metals," explained Wu. "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."

Scientists were able to lower the threshold for vanadium dioxide's electric conductivity by mixing it with other materials, like metal tungsten. Mixing also encouraged the vanadium dioxide's electrons to carry heat more effectively.

"This material could be used to help stabilize temperature," said 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."

[CardCarryingMember.VastRightWC]

In other news, researchers have discovered neurons in the brains of liberals that conduct electric currents but conduct no information of any kind.

[DIRTYSECRET]

Who is John Galt?

[Paladin2]

VO2 doesn’t sound like a metal, any more than CuO2 does.

[PCPOET7]

that’s not news most of us her at free-republic have known that for years

[Gene Eric]

Conduct heat? Opposed to generating heat?

I recall the concept of superconductors having low resistance thereby generating low heat. Similar discovery?

[The_Media_never_lie]

Who is John Galt?

Why do you ask?

[backwoods-engineer]

It’s not a metal. It’s an oxide, or it could be a ceramic.

[Oberon]

Bingo.

Vanadium? Sure.

Vanadium dioxide? Not.

[faucetman]

“....much was being propagated by the vibration of the material’s unique crystal lattices, or phonons.”

Of course it was!

(even spell check doesn’t know what phonons are)

[faucetman]

Here is an explanation for inquiring minds External control of the conductivity of correlated oxides is one of the most promising schemes for realizing energy-efficient electronic devices. Vanadium dioxide (VO2), an archetypal correlated oxide compound, undergoes a temperature-driven metal–insulator transition near room temperature with a concomitant change in crystal symmetry. Here, we show that the metal–insulator transition temperature of thin VO2(001) films can be changed continuously from ~285 to ~345 K by varying the thickness of the RuO2 buffer layer (resulting in different epitaxial strains). Using strain-, polarization- and temperature-dependent X-ray absorption spectroscopy, in combination with X-ray diffraction and electronic transport measurements, we demonstrate that the transition temperature and the structural distortion across the transition depend on the orbital occupancy in the metallic state. Our findings open up the possibility of controlling the conductivity in atomically thin VO2 layers by manipulating the orbital occupancy by, for example, heterostructural engineering. Sheesh, everybody knows that! http://www.nature.com/nphys/journal/v9/n10/full/nphys2733.html

[norwaypinesavage]

This is not possible. The Wiedemann-Franz Law has been settled science for a century and a half. It’s common knowledge that a consensus of 97 percent of scientists support the Wiedemann-Franz Law. These skeptics should be banned from publishing their drivel.

[PLMerite]

"VO2 doesn’t sound like a metal, any more than CuO2 does."

A little more O and it's shampoo:

Slow morning.

[conservatism_IS_compassion]

From Wikipedia:

The thermoelectric effect is the direct conversion of temperature differences to electric voltage and vice versa. A thermoelectric device creates voltage when there is a different temperature on each side. Conversely, when a voltage is applied to it, it creates a temperature difference. At the atomic scale, an applied temperature gradient causes charge carriers in the material to diffuse from the hot side to the cold side.

The thermoelectric effect has, IIRC, been used for ultra-low-temperature refrigeration. But the obvious limitation of the usefulness of the effect for anything other than thermocouples to measure temperature is, quote the article, “the Wiedemann-Franz Law, the rule that suggests good conductors of electricity will also be good conductors of thermal energy.”

That is, if you make a thermocouple and push a DC current through it that will result in cooling one junction of the two dissimilar metal wires and heating at the other - but if the wires you use are good electrical conductors they will also be good thermal conductors - and the conduction of heat from the hot junction to the cold junction is exactly what you do not want.

I would therefore propose - and not likely be the first to think of it - that the practicality of thermocouples and the thermoelectric effect as mechanism to achieve refrigeration/heat pumps on the one hand, and the generation of DC electric power on the other, be reevaluated with the use of VO₂ to insulate thermally but not electrically added into the mix.