High Critical Current Densities in Nb₃Sn Films with Engineered Microstructures — Artificial Pinning Microstructures

Abstract

Films with layers of Nb, Cu, and Sn have been fabricated to simulate a Nb₃Sn bronze-type process. These Nb₃Sn films have produced critical current densities greater than 1 × 10⁶ A/cm² at 4.2 K and 7.5 T. Niobium films doped with Y, Sc, Dy, Al₂O₃, and Ti have been deposited with e-beam co-evaporation onto 75 mm diameter Si wafers with a 100 nm SiO₂ buffer layer. The Nb layer was followed by a layer of Cu and a layer of Sn to complete the bronze-type process. The films with the highest J_c had about 8 vol. % Sc and about 18 vol. % Al₂O₃. Characterization of the microstructure by TEM shows that these high J_c films contained high density of inclusions about 5 nm in size and that the grain size of the Nb₃Sn is about 20–25 nm for samples heat treated at 700°C for up to eight hours.