Under pressure, sodium and hydrogen could undergo a metamorphosis, emerging as a superconductor

Jun 13, 2011

(PhysOrg.com) -- In the search for superconductors, finding ways to compress hydrogen into a metal has been a point of focus ever since scientists predicted many years ago that electricity would flow, uninhibited, through such a material.

Liquid metallic hydrogen is thought to exist in the high-gravity interiors of Jupiter and Saturn. But so far, on Earth, researchers have been unable to use static compression techniques to squeeze hydrogen under high enough pressures to convert it into a metal. Shock-wave methods have been successful, but as experiments with diamond anvil cells have shown, hydrogen remains an insulator even under pressures equivalent to those found in the Earth's core.

To circumvent the problem, a pair of University at Buffalo chemists has proposed an alternative solution for metallizing hydrogen: Add to hydrogen, they say, and it just might be possible to convert the compound into a superconducting metal under significantly lower pressures.

The research, published June 10 in , details the findings of UB Assistant Professor Eva Zurek and UB postdoctoral associate Pio Baettig.

Using an open-source computer program that UB PhD student David Lonie designed, Zurek and Baettig looked for sodium polyhydrides that, under , would be viable superconductor candidates. The program, XtalOpt, is an evolutionary algorithm that incorporates quantum mechanical calculations to determine the most stable geometries or crystal structures of solids.

In analyzing the results, Baettig and Zurek found that NaH9, which contains one sodium atom for every nine , is predicted to become metallic at an experimentally achievable pressure of about 250 gigapascals -- about 2.5 million times the Earth's standard atmospheric pressure, but less than the pressure at the Earth's core (about 3.5 million atmospheres).

"It is very basic research," says Zurek, a theoretical chemist. "But if one could potentially metallize hydrogen using the addition of sodium, it could ultimately help us better understand and lead to new approaches to designing a room-temperature superconductor."

By permitting electricity to travel freely, without resistance, such a superconductor could dramatically improve the efficiency of power transmission technologies.

Zurek, who joined UB in 2009, conducted research at Cornell University as a postdoctoral associate under Roald Hoffmann, a Nobel Prize-winning theoretical chemist whose research interests include the behavior of matter under high pressure.

In October 2009, Zurek co-authored a paper with Hoffman and other colleagues in the Proceedings of the National Academy of Sciences predicting that LiH6 -- a compound containing one lithium atom for every six atoms -- could form as a stable metal at a pressure of around 1 million atmospheres.

Neither LiH6 and NaH9 exists naturally as stable compounds on Earth, but under high pressures, their structure is predicted to be stable.

"One of the things that I always like to emphasize is that chemistry is very different under high pressures," Zurek says. "Our chemical intuition is based upon our experience at one atmosphere. Under pressure, elements that do not usually combine on the Earth's surface may mix, or mix in different proportions. The insulator iodine becomes a metal, and sodium becomes insulating. Our aim is to use the results of computational experiments in order to help develop a chemical intuition under pressure, and to predict new materials with unusual properties."

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User comments : 9

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Ober
1 / 5 (4) Jun 13, 2011
So could we make a rectangular tube with hydraulic rams on each face, compress the baby-jeezus out of it, then LOCK the rams in place, thus not requiring any further energy input, and bingo a device that could be placed on a table top, and yet be a superconductor???? If so, could we not scale this up for arterial transmission lines of AC power? Would this system need any further energy input to maintain the superconducting state?? Sounds to me like it just needs a bloody strong enclosure, and thats it????? Where is my thinking wrong????
Parsec
5 / 5 (1) Jun 14, 2011
Ober - so? We already have tons of superconductors without the extreme conditions mentioned here.

It will be interesting to find out however what conditions a mixture of sodium and hydrogen could be made to superconduct.
Bob_Kob
not rated yet Jun 14, 2011
Tonnes of superconductors? The last i heard they had to be at ridiculously low temperatures.
Mahal_Kita
5 / 5 (1) Jun 14, 2011
Ober - so? We already have tons of superconductors without the extreme conditions mentioned here.

It will be interesting to find out however what conditions a mixture of sodium and hydrogen could be made to superconduct.


Quite right.. It's all about the theory; what is superconductivity and what parameters are involved. Once you understand that, you can go look for a meta-material with the desired properties.
GSwift7
1 / 5 (2) Jun 14, 2011
This article is about basic high pressure chemistry/physics, which we actually don't know much about yet. I think it's a bit disingenuous for him to invoke the word superconductor. He's just feeding on the superconductor grant money to do important work that's only weakly associated with superconductors. The real importance of what he's doing lies in our basic understanding of high pressure chemistry/physics. Then when we learn more about that, we can compare it to what we think we know about 'normal' pressure chemistry and perhaps refine our overall understanding of both. It's great work, but as other commenters have already said, using this method to create a superconductor is kinda like going around your elbow to get to your own posterior.
GSwift7
1 / 5 (2) Jun 14, 2011
to Ober:

No, we can't maintain that kind of pressure in a volume large enough for the eye to see. The heat generated will melt just about anything other than diamond, and at 3.5 million atmospheres I don't even think a diamond would hold up for long. You're talking about containing the kind of heat/pressure that you get at the heart of a hydrogen bomb. Rather than mechanical rams, think in terms of hydrogen bombs going off on all sides to attain high pressure in the middle.
popaduhu
not rated yet Jun 15, 2011
why don't we just teleport energy ? :D
OlafMat
not rated yet Jun 15, 2011
popaduhu: We can teleport quantum state, including energy, but it takes more energy to receive it, than is teleported.
TheQuietMan
not rated yet Jun 20, 2011
The point is the pressure is used to form a stable matrix or crystal structure. Once that is done the pressure can be removed. Diamonds are a good example of this process.

I may be misreading this, but I don't think so.