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 reacti on path leading from the initial Bi(2212) phase to the final, textured Bi,P b(2223) phase. Since the formation of Bi,Pb(2223) inside the Ag sheath invo lves the presence of small quantities (less than or equal to 10%) of "trans ient" 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 heati ng above its decomposition temperature was studied at Ar/O-2 gas mixtures w ith p(O-2) less than or equal to 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 reproduct ive transformations in this system. By means of a prototype high pressure D ifferential Thermal Analysis (DTA) at pressures less than or equal to 200 b ar, a marked variation of the decomposition temperature as a function of th e total pressure was detected. The parameters for a reproducible Bi,Pb(2223) reformation after partial mel ting 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).