The influence of oxygen on the critical current densities of AgCu-sheathed Bi-2212 round wires fabricated by the melt-solidification process

Abstract Effects of oxygen on the superconducting properties have been studied on AgCu-sheathed Bi-2212 wires in long length. Two types of samples are prepared to simulate short and long length wires, i.e. samples with usual open-ends and sealed-ends. For open-ends samples, critical temperatures are varied from 87 to 82 K, when samples are heat treated under the mixed gas flow of O 2 and Ar whose O 2 volume percent varies from 13% to 100%. Critical current densities at 4.2 K and 10 T are in the same level of about 2.3 × 10 4 A/cm 2 below a O 2 volume percent of 50%. And they are decreased stepwise to about 1 × 10 4 A/cm 2 above the O 2 percent of 50%. On the other hand, for sealed-ends samples processed in air, they show nearly identical critical temperatures and degraded critical current densities, compared to open-ends samples processed under the 100% O 2 gas flow. It is found that the oxygen permeability of Ag-alloyed sheath material decreases, affecting the superconducting properties of wires.