Effect of high oxygen partial pressure heat treatment on the superconducting properties of Bi2Sr2CaCu2Ox/Ag tapes

We investigated the effect of oxygen partial pressure pO(2) during melt-and-solidification heat treatment on the superconducting properties of grain oriented Bi-2212 thick films, T-c and c-axis parameter decreased with increasing pO(2), indicating the samples were in the over-doped state. The heat treatment temperature which gave highest J(c) increased with increasing pO(2), This was explained by the increase of the solidification temperature of Bi-2212 with pO(2). Both the resistive J(c) and intergrain J(c) estimated from the de magnetization increased with increasing pO(2) when the samples were melt-solidified under an optimum condition for each pO(2). Amplitude dependence of ac susceptibility suggested that the coupling of Bi-2212 grains was improved with increasing pO(2). Irreversibility field B-irr below similar to 60 K was also enhanced with increasing pO(2). Low temperature annealing under high pO(2) after the melt-solidification also increased the oxygen content in Bi-2212 and hence B-irr. However, the annealing did not change the amplitude dependence of ac susceptibility, and transport J(c) at 4.2 K was almost independent of the annealing. The results indicate that the increase of J(c) at 4.2 K with increasing pO(2) during melt-solidification is primarily attributed to the improvement of the grain couplings. (C) 1996 American Institute of Physics.