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12/05/91

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ROOM-TEMPERATURE SUPERCONDUCTORS: KEEP LOOKING

STANFORD -- Since the 1986 breakthrough when two IBM physicists created a superconductor that worked at warmer-than- ultracold temperatures, physicists have been hunting fruitlessly for the ultimate superconductor: one that works at room temperature.

Their failure so far only means they have not yet looked in the right place, said Theodore Geballe, professor emeritus at Stanford University's Department of Applied Physics.

"I'm still hopeful," he said in a preview of his Dec. 4 acceptance speech for the 1991 Von Hippel Award, the highest honor of the Materials Research Society.

"Looking for superconductivity at room temperature is like looking for extraterrestrial life. There is plenty of space in which it might occur. We just have to know which galaxies to visit. There are too many possibilities to make random searching for superconductors a wise strategy. We should rely upon the information that already exists to provide clues for finding the star compounds."

With their lack of electrical resistance and their remarkable sensitivity to magnetic fields, superconducting materials are almost ideal for producing and using electrical energy. Already in use in the magnets for magnetic resonance imaging and planned as junctions for the next generation of computers, they have been tested in prototypes of motors, transmission lines and a train that floats above its tracks.

But there is a catch with current superconductors: The warmest temperature at which they can function is a chilly minus 234 degrees Fahrenheit. For widespread use, such as conducting electricity in homes or offices, superconductors will need to work at room temperature - about 68 degrees.

Superconductivity results when all the electrons in a compound form pairs. When electrical current travels in this paired state, the electrons are unhindered by scattering vibrations or imperfections in the conducting material.

"There are at least three classes of materials with promise for supporting superconductivity at much higher temperatures than are now possible," Geballe said.

Thin films can be built into "superlattices" by sandwiching layers of yttrium, barium, copper and oxygen with related atoms. The highly ordered atoms in these lattices promote sophisticated patterns of superconductivity. A few laboratories, including ones at Stanford, already have grown films that conduct electricity without loss at minus 297 degrees F.

A second promising class of materials comprises molecular crystals. One of these, buckminsterfullerene, is made up of 60 carbon atoms that fit together like Buckminster Fuller's geodesic domes or the panels of a soccer ball. AT&T Bell Labs discovered earlier this year that these "buckyballs" become superconducting when exposed to vapors of such alkali metals as potassium.

In a third class of materials, organic charge transfer salts, conductivity takes place along chains of organic molecules. So far in this relatively new field, superconductivity in organic chains occurs only at temperatures slightly above liquid helium.

As long as avenues such as these are being explored, Geballe said he is still "bullish on the possibility that there will be room- temperature superconductors."

dl/superconductors

This release was written by Dawn Levy, a Stanford News Service science-writing intern.

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