Effect of Ba Addition to the High-Tc Phase in the Bi-Pb-Sr-Ca-Cu-O System (V)

The effects of cooling condition and Ba addition time on Tc of high-Tc phase in the Bi-Pb-Sr-Ca-Cu-O system were studied. X-ray diffraction and DC resistance measurements were carried out to observe phase identification and Tc values for a series of samples with compositions of Bi:Pb:Sr:Ba:Ca:Cu=0.9:0.2:1.0:X:1.0:1.6(X=0-0.05). When a mixture of BaCO₃ and synthesized high-Tc phase was heated at 850°C for 60h in air, only a solid solution of high-Tc phase was formed in a quenched sample. However, in a sample cooled down slowly, Bi₃(Sr, Ba)₄Ca₃O_z was found as an impurity phase in addition to the solid solution of high-Tc phase. Mixtures of BaCO₃ (X=0.04) and the rest of metal oxides or metal carbonates were heated at 845°C 96h in air. Bi₃(Sr, Ba)₄Ca₃O_z was also found in addition to the high-Tc phase in a quenched sample. When BaCO₃ was added to the synthesized high-Tc phase, Tc(R=0) was 119K for the heated samples. When BaCO₃ was added in starting materials, Tc decreased to 110K due to the formation of Bi₃(Sr, Ba)₄Ca₃O_Z.