Phase formation in Bi,Pb(2223) tapes

Bi,Pb(2223) tapes with high critical current density (j_c) values contain up to 20% voids, which is directly correlated to the non-equilibrium reaction path leading from the initial Bi(2212) phase to the final, textured Bi, Pb(2223) phase. Since the formation of Bi,Pb(2223) inside the Ag sheath involves the presence of small quantities (⩽10%) of “transient” liquid, the question is open whether new reaction paths can be found involving larger quantities of liquid phase. The possibility of Bi,Pb(2223) phase reformation at equilibrium after heating above its decomposition temperature was studied at Ar/O₂ gas mixtures with p(O₂ )⩽0.2 bar and p(Ar) from 1 to 1´000 bar. The Pb loss was found to decrease from 1.2 to 0 at.% when applying high total gas pressures, which thus appear to be essential for the study of reproductive transformations in this system. By means of a prototype high pressure Differential Thermal Analysis (DTA) at pressures ⩽200 bar, a marked variation of the decomposition temperature as a function of the total pressure was detected. The parameters for a reproducible Bi,Pb(2223) reformation after partial melting have been studied. In the multidimensional phase diagram, other new Bi,Pb(2223) reaction paths may exist, which could be more appropriate to the fabrication of tapes with higher j_c