Effect of Constituent Contents on the Formation and Microstructure of (Bi, Pb)-2223 Phase in Partial-Melting and Sintering Process

Abstract

The influence of Bi, Sr, Ca and Cu contents on the formation and microstructure of the (Bi, Pb)-2223 phase in Bi_1.6+bPb_0.4Sr_2−aCa_2+aCu_3+cO_y, in the sintering process at 1113 K after partial melting at 1148 K for 1 h, was studied. The compositions which are slightly deficient in Sr and richer in Bi, Ca and Cu are favorable for the formation of the 2223 phase, and the optimum composition for the preparation of (Bi, Pb)-2223 phase is Bi_1.8Pb_0.4Sr_1.9Ca_2.1Cu_3.5O_y. The high-temperature microstructure held at 1148 K for 1 h mainly consisted of (Sr, Ca)₂CuO₃, (Sr, Ca)CuO₂ and a liquid phase. However, with increasing Cu content, the relative amount of (Sr, Ca)CuO₂ increased and that of (Sr, Ca)₂CuO₃ decreased. The microstructure with equal amounts of (Sr, Ca)CuO₂ and (Sr, Ca)₂CuO₃ prior to sintering is favorable for the formation of the (Bi, Pb)-2223 phase. A lot of the particle-like inclusions Sr₃PbO_x precipitated in the samples with the Sr-rich and Ca-deficient composition during the sintering process after the partial-melting. It is suggested that the precipitation of Sr₃PbO_x in large amounts in the Sr-rich and Ca-deficient samples results in a decrease of Pb content in (Bi, Pb)-2212 phase, thus slowing the formation-rate of the 2223 phase from the 2212 phase.