Reactive sintering and retrograde densification of bulk bismuth-based superconductors

Densification was observed when bulk ceramic superconductors with a composi tion of Bi1.8Pb0.4Sr2Ca2Cu3O10+delta were sintered for short times (<4 h) n ear the incongruent melting temperature. The initial shrinkage of the powde r compacts was correlated with the existence of a transient liquid phase. R etrograde densification, which is a decrease in density, occurred for longe r sintering times and was attributed to changes in pore structure. The resu lts provide direction for future processing of bulk bismuth-based supercond uctors and powder-in-tube tapes for the fabrication of long-length wire.