Superconductor Cure

The Achilles' heel of high-temperature superconducting wire in transmission cables, motors and generators lies in the wire's self-generated magnetic field. ORNL researchers recently showed that nanotechnology could offer a cure, rescuing superconductors in electrical equipment from the threat to their touted ability to conduct large currents with no resistance.

Amit Goyal and a team that included post-doctoral researcher Sukill Kang demonstrated enhancement of electrical performance in two-centimeter-long segments of high-temperature superconducting wire. They introduced defects into the superconducting film made of yttrium, barium and copper oxides (YBCO). Their method, which will likely be patented, is described in a paper entitled "High-Performance High-Tc Superconducting Wires," which appears in the March 31, 2006, issue of Science magazine. The technology received a Nano 50 Award from Nanotech Briefs, a digital magazine for design engineers.

Goyal knew that IBM researchers ten years ago reported massive enhancement of the current in single-crystal YBCO after bombarding the film with heavy-ion radiation. The radiation produced nanoscale defects that pinned the magnetic field lines when the field is aligned along the defects. But radiation is not practical and would cause the superconductor's metal template to become radioactive. Goyal's goal was to find a practical source of nanoscale defects.

The ORNL researchers mixed nano-sized barium zirconate (BaZrO3, or BZO) powder with YBCO powder to form a target. Using pulsed laser ablation, Kang heated up the YBCO target with a laser beam and deposited the oxides as a 3-micron-thick YBCO film on a flexible metal substrate. The product was a superconducting film in which the YBCO is interlaced with columns of aligned nanodots of BZO.

"Our measurements showed massive enhancement of the film's current-carrying properties," Goyal says. "We studied cross sections of the film using transmission electron microscopy. We found self-aligned nanodots arranged into separate columns. We believe each epitaxial BZO nanodot prefers to line up with the previous dot because that allows the film to be at its lowest energy state."

Goyal plans to help companies learn how to cure superconductors' greatest deficiency using these and other nanoscale defects.

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