Physicists have found a metal that conducts electricity but not heat
Researchers have identified a metal that conducts electricity without conducting heat – an incredibly useful property that defies our current understanding of how conductors work.
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Tau.Neutrino said:
Physicists have found a metal that conducts electricity but not heatResearchers have identified a metal that conducts electricity without conducting heat – an incredibly useful property that defies our current understanding of how conductors work.
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To say this is both amazing and useful is an understatement. It’s only a factor of 10 difference between theory and observation, but even a small factor could be extremely useful. What the summary article didn’t state is what the conductivity actually it. I’m going to reproduce most of this article below.
“Metallic vanadium dioxide (VO2) – a material that’s already well known for its strange ability to switch from a see-through insulator to a conductive metal at the temperature of 67 degrees C. The metal contradicts something called the Wiedemann-Franz Law, which basically states that good conductors of electricity will also be proportionally good conductors of heat.
“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.”
“Not only does this unexpected property change what we know about conductors, it could also be incredibly useful – the metal could one day be used to convert wasted heat from engines and appliances back into electricity, or even create better window coverings that keep buildings cool. Researchers already know of a handful of other materials that conduct electricity better than heat, but they only display those properties at temperatures hundreds of degrees below zero, which makes them highly impractical for any real-world applications. Vanadium dioxide, on the other hand, is usually only a conductor at warm temperatures well above room temperature, which means it has the ability to be a lot more practical.
“The thermal conductivity that could be attributed to the electrons in the material was 10 times smaller than that amount predicted by the Wiedemann-Franz Law. The reason for this appears to be the synchronised way that the electrons move through the material. The electrons were moving in unison with each other instead of as individual particles like in normal metals”
To put it another way, the electrons in VO2 are behaving as if they were both conducted and convected, whereas the heat is conducted but not convected. This reduces the heat transfer relative to the electricity transfer.
Vanadium dioxide is not a metal. It is a compound.
dv said:
Vanadium dioxide is not a metal. It is a compound.
I thought it was a crystal.
mollwollfumble said:
dv said:
Vanadium dioxide is not a metal. It is a compound.
I thought it was a crystal.
Surely you know that compounds can exist in crystal form.
dv said:
Vanadium dioxide is not a metal. It is a compound.
https://en.wikipedia.org/wiki/Vanadium(IV)_oxide
VO2 has a phase transition very close to room temperature(~66 °C). Electrical resistivity, opacity, etc, can change up several orders. Due to these properties, it has already been widely used in surface coating, sensors, and imaging. Below that temperature it’s a monoclinic a dark blue semiconducting solid, above that temperature it’s like rutile TiO2. The rutile phase is metallic.
Vanadium dioxide can act as extremely fast optical shutters, optical modulators, infrared modulators for missile guidance systems, cameras, data storage, and other applications. The phase transition between the transparent semiconductive and reflective conductive phase, occurring at 68 °C, can happen in times as short as 100 femtoseconds.
http://iopscience.iop.org/article/10.7567/JJAP.54.053201/pdf
With increased temperature, the electrical resistivity of the VO2 film decreased abruptly from 6.3 × 10−1 to 5.3 × 10−4 Ω cm across the transition temperature of around 325–340 K. The thermal conductivity of the VO2 film increased from 3.6 to 5.4 W m−1 K−1. This discontinuity and temperature dependence of thermal conductivity can be explained by the phonon heat conduction and the Wiedemann–Franz law.
Compare to the conductivity of common metals. In metallic phase it has about 1/300th of the conductivity of copper.
How come that paper says that the paper says that the Wiedemann–Franz law explains the behaviour when it patently doesn’t?