Long term anneal study and composition variation for reducing residual Bi2Sr2CaCu2Ox (2212) in (Bi,Pb)2Sr2Ca2Cu3Ox (2223) wires

Recent experiments showed that Bi₂Sr₂CaCu₂O_x (2212) intergrowths are a major current limiting mechanism in (Bi,Pb)₂Sr₂Ca₂Cu₃O_x (2223) wires and that reduced Bi₂Sr₂CaCu₂O_x (2212) correlates to enhanced critical current density J_c. We performed a final 500 h post heat treatment on commercial 2223 wire to study whether an extended heat treatment would reduce the 2212 phase content. This heat treatment did not change the 2212 content or J_c, indicating the fully processed 2223 wires were already very close to their terminal phase state. In an attempt to reduce the 2212 content, we slightly modified the standard composition in the Ca and Cu rich directions, investigating: Ca-rich; Cu-rich; Ca plus Cu-rich; Sr-poor; and Ca substitution for Sr. Although the 2212 content was not reduced by modifying the composition, the result further confirmed the correlation between J_c and residual 2212 in 2223 wires.