(Bi,Pb)-2223 phase formation in Ag clad tapes

The most promising material for fabricating long-length conductors is (Bi,Pb)-2223 produced by the powder-in-tube process in Ag clad tapes. Intensive studies have shown that the critical current density of fully processed tapes is affected by a large variety of processing parameters, but the nature of the (Bi,Pb)-2223 phase formation is still controversial. In this study certain steps of the 2223 phase formation were investigated at different stages of sintering under the influence of various temperature/time schedules of thermomechanical processing and the important role of Pb is shown. The main effects of Pb in the phase forming process are: (i) Acceleration of the 2223 formation via a rapid generation of (Bi,Pb)-2212; (ii) introduction of grain growth and texture; (iii) increase of the temperature window for the 2223 formation; (iv) decrease of reaction temperature; (v) adjustment of the hole concentration of the 2223 phase; (vi) operation as buffer for charge carriers via the temperature dependent equilibrium between Pb4+ and Pb2+; and (vii) creation of Pb containing pinning centres.