
Physicists Have Identified a Metal That Conducts Electricity But Not Heat (2017) - prostoalex
https://www.sciencealert.com/physicists-identify-a-metal-that-conducts-electricity-but-not-heat
======
Iv
That article is weirdly written and it is not clear how the title relates to
the content.

However if that metal has a good electricity conductivity and a low heat one,
wouldn't that make it an ideal candidate for seebeck-effect generators? My
understanding was that the efficency of these cells is mostly limited by the
heat conducted at the junction. If one of the metals at the junction is a heat
insulator, it should work wonders, no?

~~~
neltnerb
The way they work is by having a bimetallic junction where a temperature
difference between that junction and the other side of the wire pair is
connected causes a voltage difference.

If you were able to prevent heat from going from the hot side to the cold side
through the electrical wiring, yeah, I think the efficiency would go up. I
worked on a battery project once where the internals were over 400C, and we
needed like 000 gauge wiring which in copper meant our major thermal losses
were through our conductors.

But the article is badly written and has a bad title. The actual article is
here:

[https://newscenter.lbl.gov/2017/01/26/electricity-not-
heat-f...](https://newscenter.lbl.gov/2017/01/26/electricity-not-heat-flows-
in-vanadium-dioxide/)

and indeed they specifically mention applications to thermoelectrics. The big
takeaway was the 10x lower thermal conductivity than expected for the given
electrical conductivity.

Kind of embarrassing that the linked article on sciencealert just copy-pastes
random portions into a new article and doesn't even bother with the credits at
the bottom.

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liopleurodon
Apparently it's transparent.

I'll have to remember this the next time I need to build a whale tank

~~~
twic
> But a team in the US showed this isn't the case for 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 Celsius (152 degrees Fahrenheit).

The next time you need to do whale sous-vide, i think.

~~~
the8472
The transition temperature can be tuned with dopants[0]. And the switching
happens from transparent at low temperatures to reflective at higher
temperatures.

That said, its highest transmittance is in the infrared, it's not that great
in the visible spectrum.

[0] [https://dr.ntu.edu.sg/bitstream/handle/10220/25845/for-
your-...](https://dr.ntu.edu.sg/bitstream/handle/10220/25845/for-your-whale-
tank.pdf?sequence=1&isAllowed=y)

------
perlgeek
> The metal, found in 2017, contradicts something called the Wiedemann-Franz
> Law, which basically states that good conductors of electricity will also be
> proportionally good conductors of heat, which is why things like motors and
> appliances get so hot when you use them regularly.

Erm, no. That's not how it works.

Things become hot due to electrical and mechanical losses; if you run them
long enough, the heat moves out no matter how good or bad of a heat conductor
you use.

In fact, you usually _want_ a not-too-bad heat conductor, to avoid overheating
the active components.

That said, there are still good use cases for such a material, for example
when conducting electricity through a heat shield (furnace or freezer).

Do I want to continue reading, after the second paragraph contains such
confusing statements?

~~~
dreamcompiler
Came here to post this. Motors and appliances heat up because of friction and
because they are less-than-perfect conductors of electricity. Their good heat
conductivity is why they don't get _even hotter._

There's more:

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

Which describes a superconductor, but that word never appears in the writeup.

Subject is interesting but this article is clearly written by someone not very
familiar with the science.

------
zwsxedcrfvtgb
Is VO_{2}, a metal oxide, really a metal?

This actually annoys me a bit. Without knowings anything about it: it's a
ceramic, almost certainly a semiconductor, and since its a semiconductor it
can behave electronically like a metal under certain conditions.

Some semiconductors have poor phonon conduction, others quite good (ability to
conduct heat).

Some semiconductors have good oxygen vacancy conductivity and poor electronic
and hole conductivity. That gives you a transparent conductor.

And most ceramics are brittle. Is VO_{2} brittle?

In short, is this VO_{2} really a metal, or "just" a cool semiconductor?

~~~
neltnerb
The formal definition of a metal is just that it has overlapping conduction
and valence bands.

[https://en.wikipedia.org/wiki/Valence_and_conduction_bands](https://en.wikipedia.org/wiki/Valence_and_conduction_bands)

So it doesn't matter whether it's brittle (superconductors are brittle) or
whether it's an oxide or whether it's a ceramic as well (superconductors), or
a glass as well (metglass). What matters is that at your temperature of
interest the bands overlap so that you have free moving electrons.

But reading some other literature suggests that "metallic" VO2 is indeed a
semiconductor (not actual insulator) at lower temperatures and thermal energy
makes the electrons energetic enough to jump to the conduction band and become
a metal. So I think I'd say it's a "hot" semiconductor.

Ruthenium Oxide, Tungsten Oxide, and Chromium Oxide (at least one of them) are
also metallic, with 10-20x worse conductivity than copper. Just a weird fact I
had to figure out for a project. Actual metallic, not temperature dependent
just phase dependent (CrO2 vs Cr2O3 for instance).

On the other hand, alumina is a great thermal conductor (about 10x worse than
copper) but has almost no electrical conductivity, so I'm not so sure about
this law relating the two in the first place. I've never heard of it being a
law, I've always just treated that as a rule of thumb...

~~~
brennanpeterson
Electrical conductivity is electron motion, and if you have electrons to carry
charge, you also get thermal conductivity. So metals (in the general sense)
are good electrical and thermal conductors.

If you have very hard materials, with high phonon conduction, you can get
thermal transport via phonons. But, these are almost all poor electrical
conductors, as you need very tight binding to get hard materials with high
phonon velocity.

The prototypical example of the second case is diamond.

~~~
neltnerb
Oh yeah, fair. Good explanation. The relationship is one directional because
there are other ways to carry heat.

------
ianai
Looks like his stuff has been known about for some time. What’s kept it from
being used before now?

~~~
neltnerb
$14/kg for unprocessed V2O5, presumably VO2 is brittle.

Copper, despite all the news stories and it shooting up in 2011 (to almost
$10/kg) is today only $5.70/kg pure.

I like the idea of tuning it to act as a passive way to heat and cool homes
but compared to fiberglass insulation?

I buy thermoelectric and nonvolatile memory applications though.

~~~
the8472
One application is a thin window coating, you wouldn't need much of it. The
manufacturing process is probably more expensive than the raw material.

~~~
lightedman
This would likely not work well in desert areas over an appreciable period of
time, since most vanadium compounds are pretty soft, and desert winds tend to
contain very hard particles of silica.

~~~
neltnerb
I agree that the window application probably won't work (it's not like it's
less thermally conductive than glass anyway), but why wouldn't they just coat
the inside of the pane if they're worried about abrasive damage?

Either way, if I were to pick a technology to improve desert glass insulation
it'd be with a coating that allows in light but reflects infrared. Windows are
mostly radiative heat transport after all, you can always double pane them for
more direct conductive insulation.

~~~
the8472
It's not about thermal conductivity, it's about IR transmissivity. Above a
certain temperature it would reduce the IR transmitted to the inside, thus
keeping things cooler in the summer while still allowing the inside to be
warmed by the sun during winter.

Even in a desert the temperature-dependent behavior may be beneficial to cool
during the night. But if it is not then yes, a different, harder coating that
always reflects IR would be preferable.

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NikolaeVarius
It conducts heat, just much less than expected

~~~
emerongi
Is it possible to have a material that doesn't conduct heat?

~~~
saagarjha
The lack of a material, e.g. a perfect vacuum, as long as radiation doesn't
get involved.

~~~
duckymcduckface
Radiation becomes the dominant heat transfer mode in that case though, usually
gets really small at day to day temperatures though.

~~~
Dylan16807
It's not that small. Blackbody radiation at room temperature is 450 watts per
square meter. And it only takes an extra 15C to get 100 net watts transferred
per square meter.

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achr2
From a quick google, Vanadium also exhibits interesting properties for
superconducting. I wonder if studying these higher temperature electron
effects could impact that field..

------
dbcurtis
> which basically states that good conductors of electricity will also be
> proportionally good conductors of heat, which is why things like motors and
> appliances get so hot when you use them regularly.

NOOOOO!!!!!...... How can science reporting be so bad???

~~~
dwaltrip
Educate us please?

~~~
dbcurtis
Motors and appliances get hot because inefficiencies eventually become waste
heat. That is the source of the heat. It propagates from tbe heat source to a
surface you can feel through conduction and other mechanisms.

~~~
dwaltrip
Thanks!

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wwarner
You have to be patient and read past the inaccuracies and hyperbole in these
physics reports. This is the first I've heard of VO2 and this surprising
behavior and I think it's an amazing advance.

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unnouinceput
Quote: "The metal, found in 2017..."

Erm, say what again?

Here's wiki for vanadium, you might wanna check that year :

[https://en.wikipedia.org/wiki/Vanadium](https://en.wikipedia.org/wiki/Vanadium)

~~~
ImminentFate
They’re talking about vanadium dioxide’s transition, but it’s still a poorly
worded phrase

~~~
unnouinceput
Form wiki:

The elemental metal is rarely found in nature, but once isolated artificially,
the formation of an oxide layer (passivation) somewhat stabilizes the free
metal against further oxidation.

That's literally 2nd phrase there, right at beginning. Tell me, does that
strike you as something to be discovered only in 2017? Or the guys who made
the discover(y)/(ies) already seen VO2?

Also wiki is wrong since Vanadium is as rare as Copper. Does Copper strikes
you as something rare?

~~~
narag
Maybe he meant that "elemental metal" is redundant?

In other words: can we call "metal" anything not in the periodic table?

~~~
klyrs
Alloys of various elemental metals are also metals, but aren't elemental.

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choonway
The interior of a cathode ray tube?

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robinduckett
From 2017

