Preparation parameters governing microstructure and grain coupling of Bi2Sr2CaCu2Ox/Ag tapes prepared by partial melting

Bi2Sr2CaCu2Ox (Bi-2212) tapes have been prepared using the isothermal partial melting (IPM) method, in which partial melting and solidification are carried out at the same temperature but in different atmospheres. Maximum critical current density (J(c)) at 4.2 K under 0 T is 3.0 x 10(5) A/cm(2) and 1.9 x 10(5) A/cm(2) for the tapes prepared at 865 degrees C and 830 degrees C, respectively. This difference in J(c) is attributed to Bi-2212 grain size, which is larger in the former tape than the latter. Large grains and a rough distribution of solid phases (Bi-free and Cu-free phases) in a partially melted stare lead to large Bi-2212 grains. Amount of impurities decreases and grain coupling becomes stronger with increasing solidification time (t(s)). J(c) is saturated in tapes solidified for more than a certain time. the length in which is dependent on melt processing temperature. More time is needed to achieve saturated J(c) in tapes melted at higher temperature, because it takes longer for the large solid grains to react completely with a liquid phase in the partially melted state. It is clear that Bi-2212 grain size can be controlled by melt processing temperature, and that both amount of impurities and grain coupling strength can be controlled by solidification time. (C) 1998 Elsevier Science B.V.