Secondary phase evolution and microstructures of Bi-2223/Ag tapes prepared using powders of varying lead content

摘要

The lead content in starting precursor powders has a large impact on the evolution of microstructures and secondary phases in Bi-2223/Ag tapes. For a nominal composition of Bi_(1.8)Pb_xSr_(2.0)Ca_(2.2)Cu_3O_z when x = 0.3 and 0.35, the major secondary phase in reacted Bi-2223/Ag tapes is Pb-rich 3221, whereas it is mainly alkaline earth cuprate (AEC) phase if x = 0.2 and 0.25. Increasing the Pb content produced more liquid phase during sintering, which in turn improved the grain growth and connectivity of 2223 phase, hence resulted in the improvement of transport critical current 1c-However, excess liquid phase also favoured the formation of the Pb-rich 3221 phase, which remained as large particles among the 2223 matrix in fully processed tapes.