Comparative study on the transport critical current density of Bi-2223 and Tl-1212 Ag-sheathed superconductor tapes in low magnetic fields

Abstract

High- T c superconductor tapes with nominal compositions of Bi 1.8Pb 0.4Sr 2Ca 2.2Cu 3O 10− x (Bi-2223) and (Tl,Cr 0.15)Sr 2(Ca 0.9,Pr 0.1)Cu 2O 7− x (Tl-1212) were fabricated using the powder-in-tube method. The T c zero ’s of the tapes, which were subjected to various thermo-mechanical treatments, ranged from 100–103 K for the Bi-2223/Ag tapes and 84–86 K for the Tl-1212/Ag tapes. Their transport critical current densities in low magnetic fields (0.15 T) were compared. All the tapes are dominated by weak links where this is more severe in the Tl-1212/Ag tapes. No significant anisotropic transport properties were observed in Tl-1212/Ag tapes when the magnetic field was applied perpendicular or parallel to the tape plane (i.e. J c( H ⊥)/ J c( H ∥)=0.75–1.0). The Bi-2223/Ag tapes however show a pronounced anisotropic transport properties in applied magnetic field (i.e. J c( H ⊥)/ J c( H ∥)=0.15–0.65). This can be associated with the microstructural difference between these two types of tapes. Scanning electron micrographs reveal the slightly aligned grains in the Bi-based tapes while randomly orientated grains were observed in the Tl-based tapes.