Effect of High Oxygen Pressure Post-Annealing on the Jᵣm c-B Characteristics of Bi-2212/Ag Tapes

The effect of oxygen partial pressure, p(O/sub 2/), during the post-annealing process in the fabrication of Bi-2212/Ag tapes was investigated with respect to the critical current density, J/sub c/. High p(O/sub 2/) post-annealing was performed using encapsulation techniques, autoclave furnace and an O/sub 2/-hot isostatic press apparatus. The p(O/sub 2/) was regulated from 1 atm up to 100 atm, and the temperature of this process was fixed at 300/spl deg/C. A p(O/sub 2/) of 6 atm at 300/spl deg/C resulted in the highest J/sub 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(O/sub 2/) post-annealing promoted oxygenation of the Bi-2212 layer. High p(O/sub 2/) post-annealing improves the J/sub 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/sub c/ of the Bi-2212 layer. The degradation of J/sub c/ by higher p(O/sub 2/) post-annealing is considered to be due to the deterioration of T/sub c/. The experimental data suggest that high p(O/sub 2/) post-annealing is one of the most effective techniques for improved J/sub c/, and that post-annealing condition have to be optimized in order to obtain Bi-2212/Ag tape with the highest J/sub c/.