CRITICAL CURRENTS AND FLUX PINNING IN AG STABILIZED HIGH-TC SUPERCONDUCTOR WIRES

Y1Ba2Cu3O7-x and Bi2Sr2Ca1Cu2O8+x Ag sheathed high Tc superconductor wires have been prepared using the powder in tube technique. Characterization of wire specimens was performed mainly by measuring critical current densities at 77 K and 4.2 K, as well as by a.c. susceptibility measurements. Whereas the critical current density in Y1Ba2Cu3O7-x/Ag wires is limited by weak links, there are virtually no weak links present in Bi2Sr2Ca1Cu2O8+x/Ag wires. Above ≈20 K, critical current density in this material seems to be limited by flux creep. At lower temperatures flux creep becomes insignificant. At 4.2 K critical current densities of up to 5.7 × 104 A cm-2 in zero magnetic field and of up to 1.5 × 104 A cm-2 in a field of 26 T could be achieved, rendering possible the use of this material for very high field application. The results will be compared with those obtained on conventional metallic Nb-Ti superconductor wires. Flux pinning in these materials will be discussed, based on a model of direct summation of elementary pinning forces. © 1990.