(a) and (c): Cross-sectional TEM images of (a) 1 and 4 vol% BZO-doped films respectively. 1 and 2 vol% BZO should be the optimum levels for best performance at low fields of ~0.8 T and modest fields of ~6 T respectively, but the doping level should increase to 4 vol% at much higher fields around 15 T. (Credit: Sung Hun Wee et al., Scientific Reports)

The ability to control nanoscale imperfections in superconducting wires results in materials with unparalleled and customized performance, according to a new study from the Department of Energy’s Oak Ridge National Laboratory.

Applications for superconducting wires, which carry electricity without resistance when cooled to a critical temperature, include underground transmission cables, transformers and large-scale motors and generators. But these applications require wires to operate under different temperature and magnetic field regimes.

A team led by ORNL’s Amit Goyal demonstrated that superconducting wires can be tuned to match different operating conditions by introducing small amounts of non-superconducting material that influences how the overall material behaves.

Manipulating these nanoscale columns — also known as defects — allows researchers to exert control over the forces that regulate the wires’ superconducting performance. The team’s findings are published in Nature Publishing Group’s Scientific Reports (open access).

“Not only can we introduce these nanocolumn defects within the superconductor and get enhanced performance, but we can optimize the performance for different application regimes by modifying the defect spacing and density,” Goyal said.

A wire sample grown with this process exhibited unprecedented performance in terms of engineering critical current density, which measures the amount of current the wire can carry per unit cross-sectional area.

This metric more accurately reflects the real-world capabilities of the material because it takes into account the wire’s non-superconducting components such as the substrate and the buffer and stabilizer layers, Goyal said.

“We report a record performance at 65 Kelvin and 3 Tesla, where most rotating machinery applications like motors and generators are slated to operate,” he said.

Generating defects in the superconductor is accomplished through an ORNL-developed self-assembly process, which enables researchers to design a material that automatically develops the desired nanoscale microstructure during growth.

“When you’re making the wires, you can dial-in the properties because the defects self-assemble,” Goyal said. “You change the composition of the superconductor when you’re depositing the tape.”

The research was sponsored by DOE’s Office of Electricity Delivery and Energy Reliability. The research was supported by ORNL’s Shared Research Equipment (ShaRE) User Program, which is sponsored by DOE’s Office of Science.