IBM Breaks Barrier on Conductors : 100-Fold Increase in Electrical Load for Superconductors Told
IBM scientists have increased the current-carrying capacity of a new family of superconductors by 100-fold, thus overcoming perhaps the largest barrier to widespread use of the potentially revolutionary materials, the company announced.
The inability of such materials to actually carry large amounts of current had loomed large as, in recent months, researchers around the world made stunning progress in coming up with materials that are capable of carrying electricity virtually without resistance.
The latest breakthrough means the materials could be used “for most foreseeable applications,” said Praveen Chaudhari, vice president for science at the IBM Research Laboratory in Yorktown Heights, N.Y.
U.S. scientists have been in an international race, particularly with Japanese scientists, to develop the new superconducting materials and to incorporate them into commercial products.
Utilization of Materials
Three weeks ago, scientists at IBM reported that they had been first to make an electronic component, a highly sensitive magnetic field detector called a SQUID, from the materials.
At the same time, scientists at AT&T; Bell Laboratories in Murray Hill, N.J., reported that they had been able to fashion the brittle new superconductors into wires that are flexible enough to be wound into coils.
Friday’s results, combined with the earlier developments, suggest that American scientists are taking a lead in that race.
The new materials have far-reaching implications because they can lower the cost of using superconductivity and increase the strength of magnetic fields that can be produced. That, in turn, could sharply reduce the cost of medical imaging devices such as magnetic resonance scanners, fusion-based generators that would harness the sun’s energy, and the massive accelerators used by physicists.
They could also make possible cheaper and more efficient generation and transmission of electricity, faster and more powerful computers, and magnetically levitated trains that would glide smoothly over superconducting roadbeds.
The new development is “very exciting,” said physicist Alex Zettl of UC Berkeley. “The significance is that it makes the new materials competitive with existing superconductors. . . . That was the one thing that was holding their development back.”
IBM officials discussed the results with the news media Friday on the condition that they not be reported until today.
Superconductors are materials that lose all resistance to the flow of electricity when they are cooled below a certain temperature.
Superconductors now used commercially have critical temperatures below 23 degrees Kelvin (minus 419 degrees Fahrenheit) and thus must be cooled with liquid helium. But liquid helium is a very inefficient coolant, is difficult to handle, and is prohibitively expensive for most applications.
In December, however, scientists announced the discovery of a new family of metal oxide ceramics that had higher critical temperatures than metallic superconductors.
By February, the critical temperatures had been raised above the boiling point of liquid nitrogen (77 degrees Kelvin or minus 322 degrees Fahrenheit). Liquid nitrogen is much cheaper than liquid helium, is a much more efficient coolant and is easier to work with.
Cost Reduction
Most scientists believe that the advent of these “high-temperature” superconductors, by reducing the cost of refrigeration, will make many applications of superconductivity economically feasible.
But--until now--researchers faced a serious obstacle. Although the ceramics could carry an electric current without resistance, they could carry only a small current, similar to the current carried by household wiring. When larger currents were applied, the materials lost their superconductivity. And unless large currents can be carried, the large magnetic fields required for most applications cannot be produced.
Although some scientists feared that the low current-carrying capacity was inherent in the nature of the new materials, many believed that it resulted from the way the materials are made.
The ceramics are made by mixing together the metal compounds that are the starting materials and baking them in an oven at high temperatures for several hours. The resulting material is then ground into a fine powder, pressed into the desired shape, and re-baked. The ceramic that results still contains the granular particles.
Speculation on Reason
The IBM scientists reasoned that the limited current-carrying capacity of the ceramics occurred because these individual particles were not making very good contact, Chaudhari said.
They thus grew a large, thin-film single crystal of the superconducting ceramic, about one inch in diameter, that was not flawed by such boundaries. When they cooled it below 77 degrees Kelvin, Chaudhari said, they found that it could carry a current of 100,000 amperes per square centimeter. The best that scientists in other laboratories had been able to do previously was about 1,000 amperes.
“That’s wonderful, marvelous,” said Stanford physicist Theodore Geballe, who was the first to grow thin films of the material. “I would have thought it would have taken much longer to do that.”
When the IBM scientists cooled the thin film further, to near absolute zero, they found that it conducted a current of 5 million amperes per square centimeter--as good as the best metallic superconductors.
