Bi,Pb(2223) equilibrium and decomposition:: in situ high-temperature neutron diffraction study

The non-equilibrium reaction path which is commonly used to form the Bi,Pb(2223) phase inside Ag-clad tapes involves a small amount of a local transient liquid. New high-temperature reaction paths involving a larger amount of a stable liquid that are closer to equilibrium are needed to improve the Bi,Pb(2223)-Ag tape performance and achieve their high expected potential. In order to understand the reactions involved at high temperature during the Bi,Pb(2223) decomposition, an in situ neutron diffraction study has been carried out. Both Bi.Pb(2223) pellets and Ag-clad tapes have been melted and slowly cooled at different rates under various oxygen partial pressures. A phase analysis from the full pattern profile refinement has been performed, Bi,Pb(2223) decomposes into a Bi,Pb-rich liquid and (Ca,Sr)(2)CuO3 which is found to be the main phase at high temperature regardless of the oxygen partial pressure, Direct crystallisation of Bi,Pb(2223) from the melt has been observed in Ag-sheathed tapes and the critical current can be partially recovered after melting and slow cooling. (C) 2002 Elsevier Science B.V. All rights reserved.