BOSTON — Researchers have discovered a new family of ceramics that promise to carry much greater electrical currents than existing "high-temperature" superconductors, experts said Monday.
The new materials, discussed publicly for the first time here at a meeting of the American Assn. for the Advancement of Science, promise to bring practical applications of superconductors much nearer to reality.
The inability of the high-temperature superconductors to carry large amounts of current has been the chief problem dogging the new materials since their discovery was reported 16 months ago.
Unless superconductors can carry large amounts of current, they cannot be used for such promising applications as long-distance electric power transmission, high-speed, magnetically levitated trains and ultrafast computers.
'Very Good News'
The latest discovery, first announced in Japan and the first breakthrough in superconductor research in nearly a year, "is very good news for all of us," said physicist K. Alex Muller of IBM. Muller shared the 1987 Nobel Prize for physics for the discovery of the high-temperature superconductors.
Superconductors carry electricity with no losses due to resistance. But until 16 months ago, the only materials that could do this had to be cooled to temperatures near absolute zero (minus 459 degrees Fahrenheit) to achieve superconductivity. That is a very expensive proposition.
In 1986, Muller and J. Georg Bednorz of IBM reported that a ceramic composed of barium, strontium, copper and oxygen was superconducting at minus 396 degrees, well above existing superconductor temperatures.
That discovery touched off a race that culminated last February when Paul C. W. Chu of the University of Houston announced that a ceramic made of barium, yttrium, copper and oxygen was superconducting at minus 297 degrees. Chu's finding was crucial because it meant that the new superconductors could be cooled with inexpensive liquid nitrogen, which boils at minus 321 degrees. Cheap cooling is necessary for most potential applications of superconductivity.
Despite intensive research at laboratories around the world, scientists had been unable to find superconductors that worked at still higher temperatures.
But on Jan. 22, a Japanese financial newspaper reported that Hiroshi Maeda and his colleagues at the National Research Institute of Metals in Tsukuba had discovered a different ceramic--composed of bismuth, strontium, calcium, copper and oxygen--that is superconducting at minus 243 degrees, nearly 50 degrees higher than the existing materials.
That discovery has since been confirmed by at least half a dozen large laboratories in the United States and Europe, said physicist Praveen Chaudhari of IBM.
No one has actually measured the current-carrying capacity of the new material, said physicist John M. Rowell of Bell Communications Research in Red Bank, N.J. But researchers are confident that it will have a high capacity, he said.
The key is that the current-carrying capacity of all superconductors increases sharply as they are cooled below the temperature at which they become superconducting--the so-called critical temperature. The critical temperatures of the existing superconducting ceramics are so close to the boiling point of liquid nitrogen that researchers haven't been able to take advantage of this characteristic.
But because the bismuth compound's critical temperature is nearly 50 degrees higher, it should be able to carry a much higher current. "It would be staggering if it didn't behave this way," Rowell said.
Some evidence also suggests that the new material can be more easily fabricated into wires and other shapes than the previous ceramics, Rowell added. This would also simplify the production of practical superconducting devices.
In other developments at the meeting:
- A Massachusetts Institute of Technology researcher theorized that a storm of acid rain as poisonous as battery acid killed off the dinosaurs and other creatures 64 million years ago.
Animals deep in their burrows and creatures living in lakes with limestone bottoms might have been among the few survivors, said Ronald G. Prinn of MIT.
The new theory is a variation on a hotly debated hypothesis that an asteroid doomed the dinosaurs.
Prinn suggests that a large comet--one that makes Halley's comet look like "a little speck of sand"--struck the Earth with 1 million times more force than the world's entire nuclear arsenal.
Prinn theorizes that when the comet hit, it blasted out a crater, spewing water and rock into the air at supersonic speeds, suddenly heating the atmosphere to enormous temperatures. The heat made oxygen and nitrogen in the air combine to form nitric acid, which rained on Earth for a year.