SCIENCE / SUPERCONDUCTIVITY : Experts Turn Up Temperature in Seeking Ideal Material

The long-sought dream of room-temperature superconductivity will move much closer to reality today as French researchers report that they have achieved superconductivity at minus 10 degrees Fahrenheit.

Superconductors, which offer no resistance to the flow of electricity, hold the promise of loss-free transmission of electricity over long distances, the development of levitating trains and more powerful motors, faster computers and a host of other applications. But such developments have been stalled because superconducting materials have worked only at very cold temperatures.

Before 1986, superconductors had to be cooled to absolute zero, minus 460 degrees Fahrenheit. Then IBM researchers discovered a new class of ceramic materials that became superconducting at temperatures that were eventually increased to minus 175 degrees Fahrenheit, within the range of conventional refrigeration equipment. This was a significant advance, but still would require expensive equipment to cool the superconducting material.

The French researchers report today in the journal Science that they have made another huge leap, synthesizing a ceramic that is superconducting at temperatures 165 degrees warmer than researchers’ previous best.

The material is difficult to prepare and disintegrates when exposed to oxygen in the atmosphere, but its ability to conduct electricity at such high temperatures gives scientists confidence that they will be able to find other, more tractable materials.

“If it’s confirmed, this is one of the most exciting developments . . . in high-temperature superconductor research,” said physicist Paul C. W. Chu of the University of Houston, one of the prime movers in the original studies of the materials. “There have been reports many times of superconductivity at these high temperatures, but the data presented now is much, much better.”

The search for high-temperature superconductors has been “like looking for a needle in a haystack” without knowing for sure there is a needle, added materials scientist Theodore Geballe of Stanford University. “It’s nice to know that there is a needle.”

The 1986 discovery by IBM researchers K. Alex Mueller and J. Georg Bednorz--for which they were awarded the Nobel Prize a year later--represented a major conceptual breakthrough. Previously, superconductors were either pure metals or alloys of metals. Mueller and Bednorz found, surprisingly, that a ceramic (clay-like) material containing copper, oxygen and various other elements could also become superconducting at temperatures up to minus 175 degrees.

The ceramics were also remarkably easy to make. The ingredients were simply ground together in the proper proportions, heated in an oven to 1,000 degrees and allowed to cool slowly. The result was a material with alternating layers of different elements.

Experiments suggested that ceramics with more than three layers of copper and oxygen might work at higher temperatures, but such materials proved virtually impossible to fabricate by conventional techniques.

Physicist Michael Lagues and his colleagues at the National Center for Scientific Research in Paris followed a different and far more tedious approach, laying down one layer of material at a time, rather than mixing and baking the ingredients.

They repeated this until they had produced as many as eight copper-oxygen layers, sandwiched between layers of bismuth, strontium, calcium and oxygen.

They found that the more copper-oxygen layers they added, the higher the superconducting temperature they achieved, with the maximum being reached at eight layers.

“This compound is not very different from other compounds,” Lagues told Reuters news service Thursday. “The major difference is really the recipe, which allows us to grow the superconductor, atomic layer by atomic layer.”

The primary disadvantage of the new material, he added, is that it takes a long time to produce small quantities. Nonetheless, Lagues plans to send samples of the material to other researchers for testing in the hope that they can replicate his findings. And now that he has shown the way, others seem likely to try similar experiments. “But it’s going to be very tedious,” Chu said.

He is optimistic that, even if this compound is not what researchers are looking for, they will ultimately find one that is. “I strongly believe that (superconductivity) can happen at (room) temperature,” he said. “After all, there is no theory or experimental evidence to tell us that it can’t.”