Synthesis of Bi2223 by Low $P_{{\rm O}2}$ Sintering

Silver-sheathed Bi(Pb)2223 tapes have been developed as the first-generation high-T_c superconducting material. Generally, a long-time sintering condition exceeding 100 h at 830 ~ 845 °C in P_O2 ~ 0.08 atm has been fixed for more than 20 years to prepare Bi(Pb)2223. In addition, there are few studies on the optimization of P_O2 during sintering. In the present study, a low P_O2(= 0.02 ~ 0.03 atm) synthesis was applied for fabrication of the Bi(Pb)2223 bulks and tapes. The silver-sheathed Bi(Pb)2223 tapes were prepared by sintering under various conditions including hot isostatic pressing treatment. Fine Bi(Pb)2223 grains were observed in the samples when the first sintering was performed in P_O2 ~ 0.02 atm. This led to densification of oxide core by second sintering using hot isostatic pressing treatment (P_total = 100 atm), resulting in improvements of sharpness of superconducting transition and I_c at 77 K.