Controlled decomposition and reformation of the 2223 phase in Ag-clad (Bi,Pb){sub 2}Sr{sub 2}Ca{sub 2}Cu{sub 3}O{sub {ital x}} tapes and its influence on the microstructure and critical current density

The decomposition of almost fully reacted (Bi,Pb){sub 2}Sr{sub 2}Ca{sub 2}Cu{sub 3}O{sub {ital x}} (BSCCO-2223) tapes caused by heating in 1 atm of pure O{sub 2} at 825{degree}C has been studied. It was found that partially decomposing 2223 tapes to a mixture of Bi{sub 2}Sr{sub 2}Ca{sub 1}Cu{sub 2}O{sub {ital y}}, (Ca,Sr){sub 2}PbO{sub 4}, and other secondary phases reduced the critical current density (77 K, 0 T) from {approximately}20 kA/cm{sup 2} to nearly zero. Reheating the tapes in 7.5{percent} O{sub 2} restored the 2223 phase and, while there was some degradation of the 2223 grain alignment due to residual secondary phase growth, the critical current density was also restored to nearly its original value. We hypothesize that such a decomposition/reformation process can be useful in increasing the connectivity of polycrystalline 2223, by encouraging the formation of a liquid phase which heals residual cracks in the BSCCO core. {copyright} {ital 1996 Materials Research Society.}