The Effect of Aluminum Additions on Nb₃Sn Produced in the Solid State

Aluminum has been added to the niobium core, and in various quantities to the copper-tin bronze, of composite wires that have been reacted to form Nb₃Sn. Small amounts of aluminum in the bronze enhance the growth rate of Nb₃Sn layers; aluminum in the core, and greater amounts in the bronze displacing some of the tin, cause a reduction in growth rate. Layer thickness is a function of (reaction time)^0.67. Microprobe analysis revealed the presence of aluminum in the reacted layers only for specimens with aluminum additions to the core and in substantial quantities to the matrix. Critical current densities are primarily a function of reacted layer thickness; composition and temperature of reaction play a secondary role. Specimens in which some aluminum was successfully incorporated in thin (1- to 1.5-µm) layers of Nb₃Sn showed maximum current densities, close to 10⁹ A/m² in transverse fields of 16 T, and 7 to 8 × 10⁹ A/m² at 10 T. In fields up to 8T these materials are superior to the best reported V₃ Ga.