Evolution of the transport critical current density and irreversibility field as a function of heat treatment and pressing pressure during processing of Ag-sheathed (Bi,Pb)2Sr2Ca2Cu3Ox tapes

Abstract

Extended electric field-current density characteristics taken on the bare cores of monofilament (Bi,Pb)2Sr2Ca2Cu3Ox (2223) tapes at 77 K have been used to measure the irreversibility field, H*, and the critical current density, Jc, at different stages of tape processing. The number of heat treatments and the uniaxial pressing pressure were the experimental variables. Both H* and Jc increased substantially with heat treatment and with deformation pressure. The data are consistent with an improvement in Jc from two factors, one being an increase in the 2223 phase fraction with increasing heat treatment, the second, independent cause being an increase in the flux pinning properties of the composite. The experiments show that improving Jc involves control of at least three factors: enhancing the volume fraction of 2223 phase; increasing flux pinning; and enhancement of the connectivity of the grain boundaries that lie within the current path.