Phase Equilibrium and Formation of Bi2223 Phase in PIT-Processed Tapes

Abstract

At the final sintering process of the PIT method, a specimen with a fixed composition of Bi1.6Ph0.4Sr1.6Ca2.0Cu2.8Ox is in a six phase equlibrium state which includes the superconducting Bi2223, 35 and other phases, (when sintered at 1109 K under 0.21 atm O2.) When sintered at 1103 K under 0.078 atm O2, the six phase field changes in the region which includes the 21 phase instead of the 35 phase. During the sintering process, the supercooled liquid phase appears and reacts with the Bi2212 phase to form the Bi2223 phase. From a kinematical viewpoint, it is suggested that the intercalation of Ca and Cu progresses rapidly, after the Bi2223 phase has nucleated at the edge of Bi2212 platelets.