March 18, 2008

Supercompressed silicon and hydrogen superconducts at room temperature

A new superconducting material fabricated by a Canadian-German team has been fabricated out of a silicon-hydrogen compound [after supercompression, 96-120GPa] and does not require cooling. They had to keep the material under pressure (100GPa) in order to get it to superconduct.

CORRECTION: The press release talked about not using refrigerant and EEtimes said room temperature superconductor. They believe that the new silane / hydrogen compounds could reach room temperature superconducting levels. The temperature at which superconductivity occurs exhibits some interesting behavior. It hangs around 5-10K for most of the pressure range (50-200GPa), but in a small range between 100-125GPa, it increases quite sharply. Although the researchers only have five data points in the range and never observed a critical temperature higher than 20K, the shape of the curve indicates that, for some small range of pressures, a very high critical temperature might be achieved. So they still have to investigate the critical pressure range and possibly other compounds and still get them to work after pressure is removed. The other unpressurized material which could be superconducting at 185K are closer to being possible improved application, but they need some more independent confirmations.

So there is still work to do to make this more practical. Figure out a way to quench the metal such that it stays and metal and superconducting when pressure is removed or figure out a better but similar material. There is also the early word on the non-pressurized advances to -87C. This is at the cusp of a decent lab freezer, that easily go down to -86C. A lot of improvement and activity in the area of superconducting material seems to be happening now.

Fullerenes could theoretically be loaded with hydrogen (or other gases like silane) into the range of the correct pressure. The problem is still being able to do it and what the actual peak critical temperature is at optimal pressure The best route is probably to learn more about superconductors from these materials and then figure out a better compound that does not require these extreme efforts.

UPDATE: 3 page pdf on the methods used for the experiment.

We have used diamond anvil cell equipped with beveled diamonds and gasket made of cubic BN powder mixed with epoxy. Commercial silane of 99.99% purity (Air Liquide) was loaded trough capillaries into a small cavity surrounding diamonds where it was condensed at ≈112-150 K. All the system was carefully checked with a helium leak detector to be ensured the absolute tightness − a necessary precaution because silane is a pyrophoric substance.

Decomposition can indeed occur when silane was loaded at P<50 GPa and warmed to room temperature. In this case we clearly observed Si at the X-ray diffraction patterns, and the H2 vibron in Raman spectra even not from transparent but metallic sample at higher pressures. Thus, we avoided decomposition by loading silane and performing further measurements at low temperatures below 120-150 K. We warmed the sample up to 300 K only at pressures above 100 GPa. X-ray diffraction measurements proved that no Si phase appeared in this case. It is important that with our sensitive Raman setup we observed no hydrogen vibrons either in the sample or in the surrounding transparent cBN gasket.

This follows the recent news of higher critical temperature superconductors that are made under normal pressure at up to 185K or -87C.

"If you put hydrogen compounds under enough pressure, you can get superconductivity," said professor John Tse of the University of Saskatchewan. "These new superconductors can be operated at higher temperatures, perhaps without a refrigerant."

He performed the theoretical work with doctoral candidate Yansun Yao. The experimental confirmation was performed by researcher Mikhail Eremets at the Max Plank Institute in Germany.

The new family of superconductors are based on a hydrogen compound called "silane," which is the silicon analog of methane--combining a single silicon atom with four hydrogen atoms to form a molecular hydride. (Methane is a single carbon atom with four hydrogens).

Researchers have speculated for years that hydrogen under enough pressure would superconduct at room temperature, but have been unable to achieve the necessary conditions (hydrogen is the most difficult element to compress). The Canadian and German researchers attributed their success to adding hydrogen to a compound with silicon that reduced the amount of compression needed to achieve superconductivity.

In an article published today in the prestigious journal Science, the team has produced the first experimental proof that superconductivity can occur in hydrogen compounds known as molecular hydrides.

In related research, Tse’s team is using the Canadian Light Source synchrotron to study high pressure structures of other hydrides systems on potential superconductivity and making use of them to store hydrogen for fuel cells.

BBC News talked about that anticipated but delayed vision from the hoped for results from the 1987 "warmer" superconducting breakthroughs.

Levitating high-speed trains, super-efficient power generators and ultra-powerful supercomputers would become commonplace thanks to a new breed of materials known as high temperature superconductors (HTSC).

Those difficult to manipulate superconductors have been on track to make smaller and more efficient motors with commercial impact in 2010 South Korea was making significant advances with 1300hp superconducting generators.

They were also being tested in 36.5 MW motors for navy ships.

Here was a more recent list of predictions of what "warm" superconductors that we had before the most recent two announcements could provide. 100Tbps routers, faster communications, faster computers, better sensors and more. Room temperature versions would make all of these things cheaper, more widespread and more powerful.

If the new room temperature superconductors have or can be made to have a very high current density relative to their weight, then there is the possibility of a ground launched magnetic sail or high performance magnetic sails for space propulsion.

31 page pdf of the 1999 Zubrin study for Nasa on magnetic sails

Getting up to 100 billion to 1 trillion or more amperes per cubic meter is the current density for high performing magnetic sails.

D.G. Andrews and R.M. Zubrin, "Magnetic Sails and Interstellar Travel." Journal of the British Interplanetary Society, 1990. The first paper published, concerned primarily with the cost savings to other propulsion systems from the use of the magsail as an interstellar brake.

R.M. Zubrin and D.G. Andrews, "Magnetic Sails and Interplanetary Travel." Journal of Spacecraft and Rockets, April 1991. The technical description and very thorough analysis of the magsail for interplanetary travel. Excellent.

R.M. Zubrin, "The Magnetic Sail." Analog Science Fiction & Fact, May 1992. A version of the above paper edited for a non-technical audience. Useful for general concepts, inadequate for a full understanding.

Superconductivity in Hydrogen Dominant Materials: Silane [journal Science abstract]

M. I. Eremets,1* I. A. Trojan,1 S. A. Medvedev,1 J. S. Tse,2 Y. Yao2

The metallization of hydrogen directly would require pressure in excess of 400 gigapascals (GPa), out of the reach of present experimental techniques. The dense group IVa hydrides attract considerable attention because hydrogen in these compounds is chemically precompressed and a metallic state is expected to be achievable at experimentally accessible pressures. We report the transformation of insulating molecular silane to a metal at 50 GPa, becoming superconducting at a transition temperature of Tc = 17 kelvin at 96 and 120 GPa. The metallic phase has a hexagonal close-packed structure with a high density of atomic hydrogen, creating a three-dimensional conducting network. These experimental findings support the idea of modeling metallic hydrogen with hydrogen-rich alloy

1 Max Planck Institute für Chemie, Postfach 3060, 55020 Mainz, Germany.
2 Department of Physics and Engineering Physics, University of Saskatchewan, Saskatoon, S7N 5E2, Canada.

On leave from A. V. Shubnikov Institute of Crystallography, Russian Academy of Sciences, 117333, Leninskii Avenue 59, Moscow, Russia.

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