Phase chemistry and microstructure evolution in silver-clad (Bi/sub 2-x/Pb/sub x/)Sr/sub 2/Ca/sub 2/Cu/sub 3/O/sub y/ wires

The reaction kinetics and mechanism that control the conversion of (Bi,Pb)/sub 2/Sr/sub 2/CaCu/sub 2/O/sub z/ (Bi-2212)+alkaline earth cuprates to (Bi,Pb)/sub 2/Sr/sub 2/Ca/sub 2/Cu/sub 3/O/sub y/ (Bi-2223) in silver-clad wires were investigated as a function of equilibration temperature and time at a fixed oxygen partial pressure (7.5% O/sub 2/). Measured values for the fractional conversion of Bi-2223 versus time were evaluated based on the Avrami equation. SEM studies of partially and fully converted wires suggest: (1) the transformation to Bi-2223 is two-dimensional and controlled by a diffusion process; (2) liquid phases are present during part of the Bi-2212 to Bi-2223 conversion; and (3) growth of the (Sr,Ca)/sub 14/Cu/sub 24/O/sub 41/ phase accompanies Bi-2223 formation.<
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