Superconduction Temperatures Rising Rapidly

Scientists in Michigan have discovered a material that can conduct electricity without any losses due to resistance at 155 degrees Kelvin (minus 177 degrees Fahrenheit), or 39 degrees Kelvin above the previous record.

The researchers observed the high temperature in a new class of ceramics that has received little study. This suggests that “there may be a lot of other materials that people haven’t looked at that have higher transition temperatures,” said Steven Hudgins, director of research at Energy Conversion Devices Inc., a firm in the Detroit suburb of Troy that manufactures photovoltaic cells for converting sunlight into electricity.

The report is in the June 15 issue of Physical Review Letters.

Even Higher Temperatures

Hudgins added in a telephone interview that the researchers had seen evidence for superconductivity in the same material at 280 degrees Kelvin (45 degrees Fahrenheit). Several other groups have claimed to have seen evidence for superconductivity at such high temperatures.

Two weeks ago, for example, scientists at India’s National Physical Laboratory in New Delhi said that they had observed evidence of superconductivity at 299 degrees Kelvin (79 degrees Fahrenheit).

And physicists Alex Zettl and Marvin Cohen of UC Berkeley said they have seen evidence for superconductivity at 292 degrees Kelvin (66 degrees Fahrenheit).

Loss of Resistance

Several other laboratories have reported seeing a loss of resistance at 240 to 260 degrees Kelvin. “The problem with all of these reports,” Zettl said, “is that the superconductivity disappears when the sample is warmed up and then cooled again.”

The physics world was set on its ear last December when researchers in the United States and Japan confirmed a Swiss report that a ceramic containing lanthanum, barium, copper and oxygen became superconductive at 35 degrees Kelvin--12 degrees above the record high that had persisted since 1973.

By February, researchers had found a whole family of ceramics that became superconductive at 90 to 100 degrees Kelvin. At such temperatures, the materials can be cooled with inexpensive liquid nitrogen rather than the liquid helium required with previous superconductors.

The use of liquid nitrogen cooling may make possible many applications that would otherwise be prohibitively expensive, such as new techniques for generating electricity and transmitting it for long distances without loss, smooth-riding magnetically levitated trains and more powerful, more compact computers.

The new ceramics are composed of copper, oxygen, barium and a rare earth metal such as yttrium. Scientists now believe that sheets of copper and oxygen atoms actually carry the superconducting current and that the other metals are present primarily to hold the sheets in the proper conformation.

Substituting Atoms

Scientists have made many substitutions for the metal atoms with little success. However, the Michigan scientists replaced about every fourth oxygen atom with a fluorine atom to produce the new compound.

Such an approach has been widely discussed, but few people have reported results. In April, however, physicist Constantin Politis of the federal Nuclear Research Center in Karlsruhe, West Germany, reported that he had replaced one oxygen atom in every eight with fluorine and obtained a superconducting temperature of 116 degrees Kelvin. That remained the record until now.