Electrochemical superconductors.

Electrochemical ssuperconductors

When the stakes are high sometimes it's worth gambling on a longshot. In the race to find better ways of combining elements such as yttrium, barium, copper and oxygen to make high-temperature superconductors, that thought has pushed many researchers to try a number of novel techniques for synthesizing these materials. At the University of Illinois at Urbana-Champaign, chemist Andrzej Wieckowski and graduate student Debbie J. Zurawski are betting that electricity may do the job. They are investigating the possibility of using an electrochemical technique for synthesizing superconducting films. In the June JOURNAL OF THE ELECTROCHEMICAL SOCIETY, they report the successful incorporation of barium into a copper oxide film formed on a copper electrode, the first step toward producing a superconducting material.

The researchers dip a clean piece of copper foil into an alkaline barium hydroxide solution. Allowing the voltage applied to the foil to cycle between-1.4 and 0.725 volts produces a dark-colored copper oxide film on the foil. Analysis of the film, about 500 angstroms thick, reveals that it contains roughly one barium atom for every two copper atoms, a ratio close to that necessary for synthesizing a barium- and yttrium-based copper oxide superconductor.

In more recent experiments using a solution that also contains yttrium nitrate, the researchers have trapped both yttrium and barium atoms in a copper oxide film. However, teh trick is to end up with the appropriate proportions of yttrium, barium and copper--a goal that hasn't been achieved yet. Once a process for obtaining the correct proportions is established, then the electrochemically deposited material would be carefully dried, fired to a high temperature to create the superconducting phase and heat-treated in oxygen to ensure the right oxygen content. "Right now, the problem is getting a film that doesn't crack up when it dries," says Zurawski.

An electrochemical approach offers the advantage of providing a film with the necessary ingredients already intimately mixed at the atomic level. That degree of mixing could lower the temperature and shorten the time needed to process the film to turn it into a superconductor. Present techniques generally require the use of finely ground powders, which must be fired at a high temperature for a long time to produce the superconducting material.