Niobium-3.5tin superconductor with zirconium oxide pinning precipitates

Mark Benz at GE Research; 1% zirconium internally oxidized to form 20-30 nm zirconium oxide precipitates spaced ~100 nm apart, providing the pinning sites that gave good critical field. The case Tom was originally going to lecture on.

John Wulff had worked on niobium-titanium. Niobium-titanium had a critical temperature of about 9 Kelvin, so you were only about double that. A typical field might be six Tesla. That's okay but it's not great. Then a guy named Mark Benz, who had done his doctoral thesis here in steelmaking, went to work for General Electric Research, and they came up with niobium-3-tin. This is about what I was going to lecture on today. In niobium-3-tin, they found that if they put one percent zirconium in there, they could internally oxidize it and form zirconium oxide precipitates on a nanometer scale. I can use that term today; we didn't call them nanometer back then. They had to be like 100 nanometers apart — 20 or 30 nanometer precipitates — because that's what gave you a good critical field. If you had really pure stuff, you wouldn't get decent properties. In Backofen, the wavy slip of the niobium that had been drawn 88% — Backofen got that picture from one of John Wulff's students back in the 60s, because they were working on severely deformed niobium. My house tutor did his doctoral thesis on severely deformed niobium as a superconductor. There's a picture in here, and I showed you the wavy slip when we talked about asymmetric deformation.