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Salty superconductor champ.

Salty superconductor champ

Take a long-named compound known conveniently as ET, combine it with another ingredient and crystallize them. Squeeze the shiny black crystals with 300 atmospheres of pressure while chilling them to temperatures colder than the dark side of Pluto. The results? A new record-breaking organic superconductor.

In the Sept. 5 INORGANIC CHEMISTRY, 16 researchers from two national laboratories and North Carolina State University in Releigh report the discovery of an organic salt that loses all resistance to carrying electrical current when placed under pressure and cooled to 12.8 kelvins (-437[deg.]F) or less. The squeeze-play prevents an unwanted structural transition that would compete with the superconducting transition.

The best of the ceramic-oxide superconductors enters a resistance-free state at a relatively cozy 125 kelvins under normal pressure. But chemist Jack M. Williams of Argonne (III.) National Laboratory, who led the ET project, notes that the transition temperatures of new organic superconductors have been rising faster proportionally than those of the ceramic versions. "There's every reason to believe that the organics can have as a high a transition temperature [as the ceramics], or even higher," he says.

Salt crystals are made of matched components that donate and acdept electrons. In the record-breaking salt, layers of a chlorine- and copper-containing complex accept electrons from alternating layers of ET, otherwise known as bis(ethylenedithio)tetrathiafulvalene.

Williams' team laid claim to the previous organic superconducting record last July with a structurally similar ET salt in which a bromine complex, rather than a chlorine complex, serves as the electron acceptor. It superconducts under normal pressure at 11.6 kelvins. University of Tokyo researchers had previously reported making a related salt with a transition temperature of 11.4 kelvins.

Researchers continue to mix and match different donors and accepters in the push for higher transition temperatures. Because the resulting salts typically have about one-seventh the density of ceramic superconductors, they would be well suited for use in spacecraft and other devices requiring lightweight materials, Williams says.
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Author:Amato, I.
Publication:Science News
Date:Sep 15, 1990
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