Microstructure, impurity content and critical current density in Nb3Sn

Critical current density measurements, transmission electron microscopy and chemical analysis have established a correlation between critical current density Jc, the oxygen content in Nb3Sn and the presence of a fine dispersion of precipitate. As the oxygen content increased from <50 to 1000 p.p.m. by weight, Jc increased from 1 to 6 × 105 A cm−2 at 46 kG. A fine precipitate (particle size similar 50 A) was observed for all oxygen contents greater than 160 p.p.m. It is concluded that the precipitate particles act as flux-pinning centres in Nb3Sn. No correlation was observed between nitrogen content and Jc.