Current limiting mechanisms and phase formation in Bi,Pb(223) tapes (Invited)

摘要

Inherent mechanisms limiting j_c in Bi, Pb(2223) tapes are: the inhomogeneity of the precursor mixtures, the structural anisotropy the critical current density in c direction and the number of current carrying grain boundaries. The dominant intergrain current transfer mechanism is attributed to small-angle c axis tilt grain boundaries or railway switches. The conditions at these boundaries are influenced by the Bi, Pb(223) phase formation mechanism. In powder mixtures with free surfaces, this phase is formed by nucleation and growth, while the situation in Ag tapes is still a subject of investigation. A further limitation is given by the interruption of current paths by foreign phases.