Microstructure and Critical Current Properties of Bi-2212 Round Wires Fabricated With Different Nominal Compositions

The microstructure and superconducting properties of Bi-2212 wires seem to be strongly influenced by the nominal composition of the starting powder. We fabricated Bi-2212 round wires with different starting compositions. The highest J_c values of 175 kA/cm² at 4.2 K and 10 T were obtained in the Bi-rich sample with a Bi-rich composition. We carried out quenching experiments from the melting state of Bi-2212. We observed obviously smaller grains of impurity phases in the wire with high J_c than in the low-J_c wires in the melting state, which suggested that this is one of the reasons for the enhancement of the J_c values in these wires.