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Hot Superconductors
June 27, 2013   
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A group of chemists from the University of Warsaw has identified two chemical compounds based on silver that could be used to build a new type of superconductor capable of substantially reducing electricity transmission losses.

Countries worldwide lose a third of all electricity produced due to the electric resistance while it travels over wires made from conventional materials. If this resistance could be eliminated, billions of dollars could be saved annually in Poland alone, experts say.

Superconductors are materials that make it possible to transmit electricity while minimizing waste. But the problem is that most of these materials must first be cooled to a temperature of minus 238 degrees Celsius or less.

There are so-called high-temperature superconductors made from copper oxides. These need to be cooled down to roughly minus 100°C. This is a big difference but still a harsh subzero temperature that does not occur naturally anywhere on Earth. Besides, electricity savings are impossible since a significant amount of energy is required to cool the wires down.

The University of Warsaw researchers are aiming to design a new generation of superconductors capable of working at room temperature. They have discovered that, in the chemical compounds they have identified, quantum effects occur that enable superconductivity. The silver atoms these materials contain have a spin magnetic moment—an internal magnetic moment created by unpaired electrons. The spin can be in different directions, says Prof. Wojciech Grochala. In the compounds examined by the researchers, the spins are antiparallel and form a grid; this arrangement is identical to that in copper oxides, Grochala says. This means that the new materials can potentially become full-fledged high-temperature superconductors. But first they have to be modified so that they can conduct electricity without wastage. In order to do that, the chemists have to embed additional—so-called dopant—atoms to strengthen superconductivity in the crystalline structure of the chemical compound.

“It is known that, in the case of conventional materials containing oxygen and copper, the undoped compound (precursor) has to be doped in order to generate superconductivity in it,” Grochala says. “Doping is based on replacing some atoms of a specific kind with others. It should be exactly the same for two-dimensional silver compounds.”

The researchers do not know yet what kind of “dope” will work for silver compounds. But they say they are sure they will finally discover it. Doping is difficult because, in the case of copper oxides, it occurs outside the copper oxide layers—in other adjacent layers containing atoms of calcium, mercury or lanthanum. However, in the case of silver difluoride (AgF2), such additional layers do not exist. Work is under way to find the optimum kind of dopes and apply them.

Grochala’s research group has received about zl.2 million for its project from the National Science Center.

If the new compounds meet the researchers’ expectations and become superconductors capable of working at room temperature, the savings notched up on electricity transmission every year in Poland could total the equivalent of the country’s budget deficit, Grochala says.

Tomasz Rybicki
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