Effect of oxygen partial pressure on the superconductivity of Bi-2212 wires during post-annealing

Bi2Sr2CaCu2O8+delta (Bi-2212) silver sheathed round wire is a promising and practical material for high field superconducting insert magnet in the range of 25-30T. The effect of oxygen content of Bi-2212 on the critical current density (J(c)) of multi-filamentary Bi-221 2/Ag wires has been investigated. During the Bi-2212 wire fabrication, partial melting and solidification process was employed. Short samples which were cut from the same wire were annealed at 500 degrees C in various atmospheres for post-annealing. The morphology, lattice parameters and oxygen contents were characterized by SEM, XRD and a thermal gravimetric analyzer (TGA). The critical current (I-c) and the superconducting transition temperature (T-c) were measured by a four-probe method. Lower O-2 pressure can break the Bi-O chains, reduce the oxygen contents and change the lattice structure of Bi-2212 from tetragonal into orthorhombic. The T-c values of samples increase from 81.6 K to 91 K and the highest J(c) of samples after post-annealing is almost three times higher than that of the initial sample. (C) 2011 Elsevier B.V. All rights reserved.