Comparative studies on single crystals and superconducting Bi-(Pb)-Sr-Ca-Cu-O tapes

Comparative studies on Bi-2212 single crystal, Bi-2212 tape and 2223 tape have been carried out using AC susceptibility, magnetisation and magnetoresistivity measurements. Bi-2212 crystals have been obtained through a spiral growth mechanism using KCl as flux. Magnetisation measurements show an enhanced flux pinning in the spiral grown crystals compared with crystals grown through a layer-by-layer mechanism. The fish tail effect in M-H loop is attributable to the spirals and screw dislocations in spiral grown Bi-2212 crystals. The irreversibility line for the 2223 tape is positioned at higher temperatures than that for the 2212 tape which is in turn positioned at higher temperatures than that for the 2212 crystals. The pinning potential, U/sub o/, for 2212 tape, determined by using resistance measurements in magnetic fields, is smaller than that of Ag/Bi-2223 tapes but larger than that for 2212 single crystals. These results indicate that the defects induced by mechanical deformation or spiral growth act as pinning centers in Bi-based materials, responsible for the improvement in flux pinning.