Researchers Tell Major Advance in Conduction
For the third time in two months, scientists have announced a significant advance in the development of new materials that display no resistance to the conduction of electricity, and more advances are expected soon.
But the most recent achievement, announced in Washington over the weekend by the National Science Foundation, was termed a “major breakthrough” by the foundation because it increases the temperature at which the materials become superconducting above the boiling point of liquid nitrogen.
That temperature has been something of a “Holy Grail” for physicists studying superconductivity because liquid nitrogen represents an inexpensive, widely available way to cool large electrical equipment.
The new development thus represents the potential for significant reductions in the cost of generating electricity and transporting it for long distances, of the magnetic imaging devices now used in hospitals, and of the large electromagnets used to build accelerators for high-energy physics. The new materials might also speed the introduction of smooth-riding, high-speed trains that would be magnetically levitated above superconducting tracks.
The new technology might also make possible faster, much less expensive supercomputers of the type used for weather prediction or for the control of anti-missile defenses in President Reagan’s Strategic Defense Initiative.
The rapidity with which researchers have been able to increase the temperature of superconducting metals has some physicists here at a meeting of the American Assn. for the Advancement of Science talking excitedly about the possibility of materials that become superconducting at room temperature.
Only a year ago, such talk would have been considered the wildest form of speculation.
“It’s very exciting,” said Leon M. Lederman, director of the Fermi National Accelerator Laboratory. “It looks like it’s going to keep changing every month for a long time.”
Superconductivity was discovered at the turn of the century when it was observed that lead and mercury lost all their resistance to an electrical current when they were cooled to temperatures of a few degrees above absolute zero (minus 460 degrees Fahrenheit), the point at which, theoretically, all motion of atoms ceases.
In contrast, even such good conductors as copper and silver show some resistance to the passage of electricity. In electric power transmission, for example, 10% to 20% of power is converted into heat over long distances due to resistance.
By the early 1970s, scientists had succeeded in increasing the temperature at which certain metallic alloys became superconducting to about 23.2 degrees Kelvin (minus 419 degrees Fahrenheit). They were then unable to raise the temperature higher, leading many physicists to despair of future breakthroughs.
In April, 1986, scientists at the IBM Zurich Research Laboratory in Switzerland announced that they had seen traces of superconductivity at temperatures above 30 degrees Kelvin. They achieved this with a complex mixture of barium, lanthanum, copper and oxygen.
At the end of December, physicists Paul W. C. Chu and his colleagues at the University of Houston and Robert J. Cava and his associates at the AT&T; Bell Laboratories in Murray Hill, N.J., simultaneously announced that they had achieved superconductivity at temperatures of 36 to 40 degrees Kelvin with variants of the same material.
At the end of January, Chu announced the discovery of a similar material in which barium had been replaced by strontium. This material became superconducting at 52.5 degrees Kelvin.
The newest development was achieved jointly by Chu and physicist Maw-Kuen Wu of the University of Alabama at Huntsville. Their new material became completely superconducting at a temperature of 94 degrees Kelvin, well above the 77-degree boiling point of liquid nitrogen.
“We have seen some transient superconductivity at a temperature of 240 degrees Kelvin,” Wu said in a telephone interview, “and there is a chance we can get it closer and closer to room temperature.”
They refused to reveal the composition of their material pending the publication of a paper that is scheduled to appear in the March 2 issue of Physical Review Letters.
The importance of being able to use liquid nitrogen for cooling was emphasized by the National Science Foundation. The foundation said that cooling with liquid nitrogen is only one-tenth as expensive as cooling with liquid helium, which is now used routinely for superconducting magnets, and that a given amount of liquid nitrogen is 20 times as efficient a refrigerant as liquid helium.
Physicist Chris Quigg of Fermilab called the development of the new materials “revolutionary,” but cautioned that it will be some time before their impact is felt. “There was a 15-year period between the time the current niobium-titanium (superconducting) alloys were discovered in the laboratory and the time they came into regular use.”
