Effect of high oxygen pressure post-annealing on the Jc-B characteristics of Bi-2212/Ag tapes

The effect of oxygen partial pressure, p(O₂), during the post-annealing process in the fabrication of Bi-2212/Ag tapes was investigated with respect to the critical current density, J_c. High p(O₂) post-annealing was performed using encapsulation techniques, autoclave furnace and an O₂-hot isostatic press apparatus. The p(O₂) was regulated from 1 atm up to 100 atm, and the temperature of this process was fixed at 300°C. A p(O₂) of 6 atm at 300°C resulted in the highest J_c at 4.2 K. This result is consistent for the three different post-annealing techniques. A distinctive change in microstructure was not observed even though the high p(O₂) post-annealing promoted oxygenation of the Bi-2212 layer. High p(O₂) post-annealing improves the J_c of Bi-2212/Ag tape by decreasing electromagnetic anisotropy in the oxide layer. However, an increase in excess oxygen content produces not only a decrease in the electromagnetic anisotropy, but also a decrease in T_c of the Bi-2212 layer. The degradation of J_c by higher p(O₂) post-annealing is considered to be due to the deterioration of T_c. The experimental data suggest that high p(O₂) post-annealing is one of the most effective techniques for improved J_c, and that post-annealing condition have to be optimized in order to obtain Bi-2212/Ag tape with the highest J_c.