Posted on 09/04/2001 5:40:22 PM PDT by Lessismore
In the mid-1980s, the discovery of 60-atom carbon spheres (C60) and high-temperature superconductors came as two major surprises. Now an international trio of researchers led by physicist Hendrik Schön of Lucent Technologies' Bell Laboratories in Murray Hill, New Jersey, has combined these two feats. In a paper published online this week by Science (www.sciencexpress.org), Schön's team reports that by placing a crystal of C60 spiked with other compounds in the heart of a transistor, they can turn it into a high-temperature superconductor capable of conducting electricity without resistance up to 117 kelvin (K).
"This is huge," says Art Ramirez, a condensed matter physicist at Los Alamos National Laboratory in New Mexico. C60-based transistors spiked with new compounds might well superconduct at higher temperatures, perhaps even at room temperature, Ramirez says. Moreover, the crystals that Schön's team created are far easier to craft into electronic components than the standard high-temperature superconductors made from copper oxide-based ceramics, a property that could pave the way to new high-speed computers based on the technology. "This is what people have been trying to do all along" with high-temperature superconductors, Ramirez says.
This week's report follows up a discovery that Ramirez, then at AT&T Bell Labs, and colleagues made in 1991. The researchers found that crystals made of the soccer ball-shaped C60 molecules would superconduct at 18 K if they were spiked with alkali metals to make them better conductors of electrons. Superconductors can also work by conducting positively charged "holes," which are essentially electron vacancies in a material. In the late 1990s, Schön and his colleagues began to suspect that they could push the threshold temperature for superconducting (called the critical temperature, or Tc) higher if they could coax the C60 to conduct holes instead of electrons. Doing so, they and others determined, would increase a property in the material known as the density of states, the number of charges the material can harbor at key energy levels. That number is closely tied to the superconducting temperature.
Boosting the number of holes in C60 was difficult. The traditional strategy of doping the material with other compounds--in this case, ones that added holes--made the C60 crystal fall apart. But last year, Schön and Bell Labs colleagues Christian Kloc and Bertram Batlogg hit upon a novel solution: building a transistor around the crystal and using its charge-carrying ability to flood the crystal with holes. The scheme worked. As the trio reported in the 30 November issue of Nature, the C60 transistor started superconducting and kept it up at temperatures as high as 52 K.
This week's report, which more than doubles that record, shows that Schön and his colleagues had another trick up their sleeves as well. This time they added another way of increasing the material's density of states: expanding the distance between individual C60 molecules in the crystal, a property known formally as the material's lattice constant. C60 has a lattice constant of 14.15 angstroms. "If you expand the lattice, the density of states becomes larger and the Tc increases," says Schön.
According to Schön, Kloc--the group's crystal grower--tried numerous additives and ultimately hit on two compounds, trichloromethane and tribromomethane, that did the trick. The former expands the lattice constant to 14.29 and the latter to 14.45. The compounds hiked the material's density of states, touching off an exponential increase in Tc.
That huge jump bodes well for researchers, Ramirez says. "They need to expand [the lattice constant] to something like 14.7, and that will be room temperature." So far, nobody knows whether any additive will push C60 to that magic number without making the crystal fall apart. But now that the word is out, other groups are sure to try their luck. "This is a footrace now," Ramirez says.
Even if C60 proves not to be a room-temperature superconductor, it could still have a big impact on applications. Ceramic superconductors are "extremely difficult" to fashion into transistors and other electronic components, Ramirez says, because the interfaces where they join with other materials typically harbor imperfections that trap electric charges moving through the devices. The problem can be overcome by growing devices one atomic layer at a time. But that's difficult and costly.
Organic materials appear far more forgiving, Ramirez says: "With essentially a shoestring effort, [Schön's team] gets incredible device quality and performance." Because superconducting electronics are extremely fast and are ideal for detecting minute magnetic fields, a new supply of C60-based superconducting devices could revolutionize fields as disparate as high-speed computing and medical imaging. For researchers of all stripes, that would be another welcome surprise.
The EPA essentially banned the industrial use of this stuff nearly a decade ago. I guess we've finally hit the point where regulation proceeds invention.
http://news.independent.co.uk/business/news/story.jsp?story=92371
Motorola unveiled a microchip that is up to 40 times faster than existing technology yesterday, in a move that the US mobile phones and chip giant hailed as the most important breakthrough in the industry since the 1950s.
It wasn't so long ago that they got to 40 degrees kelvin, big news at the time. Expensive cooling systems are still needed at 40 degrees. But the higher the critical temperature, the simpler the cooling. That leaves 156 degrees to go to zero, which many household game freezers can attain.
American Superconductor Corporation (Nasdaq: AMSC, news, msgs) today announced it has built and demonstrated the world's first 5,000-horsepower (hp), high temperature superconductor (HTS) electric motor. The company's patented, ultra-compact HTS electric motors (see http://www.amsuper.com/5000htsmotor.htm) are designed to reduce manufacturing costs of industrial and ship propulsion motors by up to 40 percent compared with conventional motors. The electrical losses of HTS motors, which utilize HTS wires instead of copper wires on the rotor, are also much lower, which translates into significant fuel savings and lower operating costs.
American Superconductor's prototype 5,000-hp HTS motor is about the size of a household refrigerator. It is as little as half the size and weight of a conventional 5,000-hp motor. Its net electrical losses, including losses associated with cryogenic cooling of the HTS wires, are up to half the electrical losses of a conventional motor.
Motors over 1,000 hp utilize approximately 25 percent of all electric power generated in the United States. The Department of Energy estimates that the lower electrical losses of HTS motors could save U.S. industry billions of dollars per year in electrical operating costs.
"HTS technology opens the door to radically new designs and market opportunities for electric motors and for the industrial and transportation systems in which they are utilized," said Greg Yurek, chief executive officer. "By delivering more power in a smaller package that operates with lower electrical losses at essentially the same price, we are creating entirely new value propositions for our customers."
Yurek added that American Superconductor's Electric Motors and Generators business is focused on development and commercialization of electric motors over 1,000 hp and electric generators over 10 megawatts. Electric generators involve essentially the same technology as motors. "We plan to field additional prototype motors and generators over the next two years and we are on track for commercial sales in 2004," he said.
Industry experts estimate that the current market for industrial electric motors with power ratings over 1,000 hp, used in applications such as pumps, fans and compressors, is approximately $1.2 billion per year worldwide. A major new market emerging for high-power electric motors is electric ship propulsion. According to industry experts, the current annual global market for electric motors utilized for electric propulsion in commercial cruise and cargo ships is approximately $250 million. The market for ship propulsion motors is expected to grow rapidly to over $1 billion per year by 2010 because electric drives are becoming the propulsion system of choice for both commercial and Navy ships. American Superconductor is currently working under a contract from the U.S. Navy's Office of Naval Research to design and develop HTS ship propulsion motors up to 33,500 hp for application in electric warships (see http://www.amsuper.com/navyupdate.htm). The company expects sea trials of its HTS ship propulsion motors by the end of 2003.
The HTS Advantage
American Superconductor's new 5,000-hp motor, an alternating current (AC) synchronous, "air-core" design, utilizes HTS wires for the field windings on the rotor instead of copper wires. The company's HTS wires carry over 140 times more electricity than copper wires of the same dimensions, a feature that has allowed radical design changes in industrial and ship propulsion motors, and in the systems in which these motors are employed. The HTS wires in these motors carry electricity with no electrical losses when cooled to cryogenic temperatures. A cryo-refrigerator is used to cool just the HTS windings. Including the power needed to operate the cryo-refrigerator, the electrical losses for HTS motors are up to half those of a conventional motor. Ultra-compact HTS motors, including the cryo-refrigerator, are one-half to one-fifth the size of conventional motors.
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