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Explaining Superconductivity In Magnesium Diboride

January's discovery of high-temperature superconductivity in magnesium diboride, a common laboratory compound, has set scientists scrambling to understand the phenomenon, said physicist Warren Pickett of the University of California, Davis.

Using a computer model, Pickett and graduate student Joonhee An have come up with an explanation of how this superconductivity occurs.

Superconductors have essentially no resistance to electrical current. They are used to make powerful magnets, used for example in medical magnetic resonance imaging (MRI) machines. Their use is limited by the need for cooling to almost absolute zero (less than minus 450 F) with liquid helium.

In 1986, scientists discovered that some ceramic compounds became superconductors at higher temperatures, around minus 390 F. While this is still pretty cold, this jump in operating temperature represented a major advance. However, these materials were expensive to produce and difficult to make into wire, said Pickett.

Theoretically, there's no reason that room temperature superconductivity should be impossible, he said.

On Jan. 10 this year, Japanese scientist Jun Akimitsu announced that magnesium diboride became superconducting at minus 389 F. As well as being relatively cheap, magnesium diboride is a metal which seems to have encouraging properties for some applications, said Pickett.

After hearing of the discovery, Pickett's lab began to model the behavior of magnesium diboride crystals, which are made up of alternating layers of magnesium and boron atoms. They found that while the atoms in each layer are held together by strong chemical bonds, the structure and composition of magnesium diboride makes these bonds act as if they were metallic bonds. These metallic bonds contribute to the superconductivity of magnesium diboride.

"We need to look at more layered materials like this, that are metallic or that can be made metallic. There's no reason we can't find materials that are still better superconductors," said Pickett.

Pickett and An's paper is to be published in Physical Review Letters.

[Contact: Warren Pickett, Andy Fell]






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