Correlation of critical current density and phase conversion at different final cooling rate in Ag-sheathed PbBi2223 tapes

摘要

As shown by Parrell et al., a final reduced cooling rate can produce an improvement of the optimum critical current in field. In this paper we present results on the critical current density and magnetic field dependence of Ag-sheathed (Pb,Bi)-2223 multifilamentary tapes as a function of the final sintering time for different cooling. Correlation between 2223 phase conversion, as determined by XRD, and the critical current density is also examined. For samples slow cooled to 800/spl deg/C at 1/spl deg/C/h followed by furnace cooling to room temperature, the critical current density remained almost constant at 20 KAcm/sup -2/ with different final sintering times between 10 to 150 hours. In contrast samples slow-cooled to 730/spl deg/C at 1/spl deg/C/h showed a decreased J/sub c/ of 7 KAcm/sup -2/ for a short final sintering time of 10 hours, rising gradually to 22 KAcm/sup -2/ at 200 hours. Corresponding to this, the samples cooled to 800/spl deg/C show a phase composition of 90% apparent (Pb,Bi)-2223 for all times, as opposed to a gradual increase of the (Pb,Bi)-2223 phase from 65% to 90% with increasing sintering time for samples slow cooled to 730/spl deg/C. As the conditions are exactly the same prior to the cooling below 800/spl deg/C, the reduced conversion for the samples slow cooled to 730/spl deg/C must be the result of 2212 precipitation from the apparent (Pb,Bi)-2223 phase present at 800/spl deg/C.