High-Field Nb₃Sn Superconductors Prepared through a New Route

Abstract

Nb₃Sn superconductors have been prepared through Nb₆Sn₅ compound powder synthesized by a melt diffusion process from Nb and Sn powders. The Nb₆Sn₅ powder was mixed with Nb powder in a ball mill. The resulting mixed powder was encased in a Ta tube, and fabricated into a tape. The mechanical mixing of Nb₆Sn₅ and Nb powder promotes the formation of A15 Nb₃Sn phase in the subsequent heat treatment, and improves superconducting performance. The NbsSn tape shows an upper critical field Bc₂ of nearly 25T at 4.2K after the reaction at 900°C. The Bc2 is still increased by Ti doping. A small amount of Cu addition decreases the optimum reaction temperature to 850°C. Present Nb₃Sn specimen exhibits considerably larger normal state resistivity than that of bronze-processed M>3Sn, which may be the origin of enhanced Bc2 in the present Nb₃Sn specimen.