In-situ high temperature neutron diffraction study of Bi,Pb(2223) phase formation in Ag-sheathed monofilamentary tapes

High temperature neutron diffraction measurements were performed on Bi(2223 )/Ag-sheathed monofilamentary tapes at the ILL high- flux reactor in Grenob le. Reactions leading to the conversion from Bi(2212) to Bi,Pb(2223), as we ll as other transformations involving secondary phases, were directly obser ved during the reaction heat treatment. The heating ramp and annealing cond itions were exactly the same as those used for standard high-performance ta pes processing. A quantitative analysis was carried out by means of a full- pattern profile refinement technique: up to 7 phases were simultaneously de tected and successfully refined. An increase of the Bi(2212) phase during a slow cooling was found not to be related to a decomposition of Bi,Pb(2223) , which remained stable during cooling. The role of secondary cuprates, in particular (Ca,Sr)(14)Cu24O41, was investigated. Since neutron diffraction allows for an absolute measurement of the weight of crystalline matter insi de the sample, it was possible to measure the total crystalline matter amou nt as a function of temperature and time during processing. Evidence of par tial melting at high temperature was found, strongly supporting the Bi,Pb(2 223) formation via a nucleation-and-growth mechanism at the early stage of the process.