Very high upper critical fields and enhanced critical current densities in Nb₃Sn superconductors based on Nb–Ta–Zr alloys and internal oxidation

Abstract The inhibition of Nb 3 Sn grain growth in the presence ZrO 2 nanoparticles appears to be one most promising method for pushing critical current densities superconducting wires levels that meet requirements set Future Circular Collider. We have investigated effect formed by internal oxidation Zr on properties and microstructure from Nb-1 wt%Zr, Nb-7.5 wt%Ta, wt%Ta-1 wt%Zr wt%Ta-2 alloys. A monofilamentary wire configuration was used, with a 0.22 mm outer diameter Nb-alloy tube containing core powdered metal oxide (SnO , CuO or MoO ) as oxygen source successive deposits Cu, Cu surface. As determined inductive measurements, layer samples based alloys internally oxidized were superior those wt%Ta. showed higher at high magnetic fields (above 10–15 T), upper exceeding 28.5 T 4.2 K (99% normal state resistivity criterion). record value 29.2 field obtained wt%Zr. Hypotheses are proposed discussed explaining this unexpected increase field, considering possible effects non-oxidized formation microchemistry Sn. Regardless sample type grains observed our an aspect ratio 1.5–1.7. When compared short axis direction, mean distance between boundary intercepts (lineal intercept method) is ∼40% smaller than reference In long direction reduction 20%–30%.