Microstructure and superconducting properties of Bi-2212/Ag tapes

In order to understand the effects of processing parameters on the formation of Bi-2212 phase and to improve superconducting properties, Bi2212 (nominal composition Bi₂Sr₂Ca₁Cu ₂O_x), sheathed with silver was fabricated and thermo-mechanically treated for this study. Scanning electron microscopy was employed to investigate the phases and microstructure at different stages of the Bi-2212 formation and in the final materials. A SQUID magnetometer was used to characterize the T_c of the conductors. Voltage-current (V-I) characteristics were measured with a standard four-probe method at 77 K in different magnetic fields in order to improve the correlation of magnetic properties to microstructural properties. The critical current density is ~15000 A/cm² at 77 K self field. The critical current distribution in the conductors was studied by computing the second differential of the VI curves and the correlation between the microstructure and the second differential was analyzed. The current transfer to the metal sheath and the effect of the sheath on the shape of the VI curve are discussed