Development of high critical current density in multifilamentary round-wire Bi2Sr2CaCu2O8+δ by strong overdoping

Bi 2 Sr 2 CaCu 2 O 8 + δ is the only cuprate superconductor that can be made into a round-wire conductor form with a high enough critical current density Jc for applications. Here we show that the Jc(5 T,4.2 K) of such Ag-sheathed filamentary wires can be doubled to more than 1.4×105 A/cm2 by low temperature oxygenation. Careful analysis shows that the improved performance is associated with a 12 K reduction in transition temperature Tc to 80 K, an increase in flux pinning, and particularly a significant enhancement in intergranular connectivity. In spite of the macroscopically untextured nature of the wire, overdoping is highly effective in producing high Jc values.