Improvement of superconductors within reach

Jul 09, 2010
Improvement of superconductors within reach
The image shows atomised positions along a grain boundary. The red line to the right shows the charge density along this boundary.

An international group of physicists from the University of Augsburg in Germany, the University of Florida in Gainesville, and the Niels Bohr Institute at the University of Copenhagen have succeeded in creating a theoretical modelling of the microscopic defects in superconductors and in discovering the main cause for the drastic drop in the electric current. The results have been published in the internationally recognized scientific journal, Nature Physics.

In a time where the political and scientific discussion is focused on the global crisis, research is being done on alternative techniques for the production of energy and new ways of reducing energy consumption. A superconductor is based on a complex and can be used to transport energy with minimal energy loss.

Low temperature gives low resistance

The phenomenon of has been known for almost a century, but the problem up until now has been that superconductors can only function at very low temperatures - temperatures that are very difficult to achieve. The first superconductors were cooled to a few degrees above (minus 273 degrees Celsius).

It was only 25 years ago that the use of superconductors for electricity came within reach. It was discovered then that the superconducting properties of some compounds could be improved by cooling liquid air at very low temperatures. Today, we are up to around minus 140 degrees Celsius with copper oxide materials.

Small defects causing major damage

But you run into another obstacle in the use of superconductors - the microscopic defects that are found in almost all materials. The small defects on the boundary between the individual, affect the transport of electric current in the superconductor. Up until now no one has succeeded in developing a theoretical understanding of this phenomenon even though the effect is well known from experiments and even though there are also various methods for improving the physical properties of the materials.

Theoretical understanding

"We have now made a theoretical modelling of the microscopic defects in these materials and simulated a superconducting current. We have managed to identify an accumulated electrical charge on the boundary between different misoriented crystal axes, as the main cause of the drastic drop in the electric current", explains physicist Brian M. Andersen, Niels Bohr Institute at the University of Copenhagen.

The theoretical understanding of high temperature superconductors can now be used for further research into methods that can improve the transport of energy in copper oxide materials, research that ultimately could lead to the use of high energy superconductors for supplying electricity.

Explore further: Electron spin could be the key to high-temperature superconductivity

More information: Read the publication in Nature Physics.

Provided by Niels Bohr Institute

4.5 /5 (17 votes)

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fmfbrestel
4 / 5 (1) Jul 09, 2010
Not that the theory isn't important, it is -- knowing why something is happening can greatly improve your chances of finding solutions. However, while they were making computer models -- read the other main page article on superconductivity -- some cambridge researcher was busy not only increasing the current flow, but also lowering the cost of YCBO.
eachus
not rated yet Jul 09, 2010
Some Cambridge researcher was busy not only increasing the current flow, but also lowering the cost of YCBO.
Actually the Cambridge work is on both creating single crystal YBCO--so there are no grain boundaries--and on adding impurities like U238 to create flux pinning sites once the grain boundaries are gone. The lower cost part is that their process for creating monocrystaline YBCO is much cheaper than any other way of getting YBCO crystals.

Why add impurities? Decades ago it was discovered that some impure superconductors had a much higher critical current. Superconductors exclude magnetic fields. (So how do you use superconductors to create a magnetic field? Simple the current does not flow through the bulk material but only on the surface. This happens with ordinary conductors too.) When the magnetic field is high enough the field goes through small non-superconducting spots at the impurities, and the bulk of the material is unaffected.
Jigga
not rated yet Jul 10, 2010
the current does not flow through the bulk material but only on the surface. This happens with ordinary conductors too.
This is true for type I superconductors only - those of type II ones (like the YBaCuO) allow penetration of magnetic field to the bulk phase through flux lines. The magnetic field passes superconductor through the lattice of Abrikosov vortices.
This happens with ordinary conductors too
Only at AC due the skin effect.
xamien
not rated yet Jul 11, 2010
I very eagerly look forward to experimental tests of the new theory. If they've finally figured it out... how exciting!
eachus
not rated yet Jul 11, 2010
the current does not flow through the bulk material but only on the surface. This happens with ordinary conductors too.

This is true for type I superconductors only - those of type II ones (like the YBaCuO) allow penetration of magnetic field to the bulk phase through flux lines.
The problems with editing down to 1000 characters. I took out the type I/type II explanation. And technically the pinned flux lines don't penetrate the superconductor--they penetrate the solid material. The points where the flux is pinned are non-superconducting.

This happens with ordinary conductors too...
Only at AC due the skin effect.
I wish it were true. I used to spend a lot of time improving the material around copper and other conductors to deal with this. (Retired now.) Yes, the DC signal in a wire will travel through the center of the wire, but it also travels in the dialectric, and you don't want them to separate, even in the ground and power traces.
Jigga
not rated yet Jul 11, 2010
The superconductor has the higher transition temperature Tc, the more separated are layers with hole atoms withing superconductors by semiempirical Roser's equation:

http://tinyurl.cz/u47

But the larger separation of hole stripes within superconductor is, the lower probability is, these stripes will form a continuous phase in polycrystalline material.

http://tinyurl.cz/u49

This is the reason, the critical current of common superconductor samples decreases the more, the higher is their Tc.
Jigga
not rated yet Jul 11, 2010
Ideal superconductor will be formed by sparse, but continuous mesh of copper atom stripes embedded into oxide layers.

You can think about hole stripes like about high pressure channels or pipes for superconductive electrons. The higher electron pressure we can achieve inside of them, the higher the critical temperature will be. The higher electron pressure exists inside of superconductor hole stripes, the thicker must be the surrounding layer of atoms, which hold electrons together. It means, the superconductor has the higher Tc, the more are hole stripes with copper atoms separated in it.

The role of impurities is complex, but in general, the more atoms the crystal lattice contains, the higher is the Tc. This is because complex mixtures of atoms forms crystals more difficult and their crystal planes with hole stripes are more separated. Because electrons are heavily compressed inside of hole stripes, the bulk or atoms around them makes whole structure more robust.

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