High-Field A-15 Superconductors Prepared from Intermediate Compound(High Field Superconductors)

Abstract

A15 Nb_3(Al, Ge) and Nb_3Sn have been easily synthesized starting from Nb_2(Al, Ge) and Nb_6Sn_5 intermediate compound powder, respectively. The intermediate compound powder was mixed with Nb powder by a ball mill in Ar atmosphere. The mixed powder was encased in a Nb or Ta tube, and then fabricated into a tape without intermediate annealing. The mechanical mixing of powders promotes the formation of A15 phase in subsequent reaction treatment. The bulk sintered specimens show higher onset T_c but broader T_c transition than tape specimens. In the Nb_3(Al, Ge) tape reacted at 1300℃, a J_c of over 2.7×10^4 A/cm^2 has been obtained at 4, 2K and 23T. The addition of MgO powder enhances J_c and reduces the peak effect in the Nb_3(Al, Ge) tape. The T_c of Nb_3Sn tape prepared by present process is appreciably higher than that of bronze-processed Nb_3Sn. Even pure Nb_3Sn tape shows Bc_2 of nearly 25T at 4.2K after the reaction at 900℃. The present A15 Nb_3(Al, Ge) and Nb_3Sn tapes seem to be promising for generating 20T at 4.2K

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