Ramp rate effect in Bi/sub 2/Sr/sub 2/Ca/sub 2/Cu/sub 3/O/sub 10+/spl delta// formation

The properties of Ag-sheathed Bi2223 tapes depend strongly on the thermomechanical treatment processing parameters. We have examined the conversion of precursor powders to Bi2223 in heat-treated tapes as a function of ramp-to-temperature rate. Tapes containing precursor powders were ramped at rates from 50/spl deg/C/h to 800/spl deg/C/h to a final temperature of 835/spl deg/C, then held for 50 h, all in 20% O/sub 2/ and 80% N/sub 2/. The composition of the tapes was then determined by X-ray diffraction and by low-temperature magnetization measurements. The heat-treated tapes consisted almost entirely of a mixture of Bi2212 and Bi2223. The volume ratio of Bi2223 to Bi2212 in the tapes depended on the ramp rate in a complicated way; the volume ratio was largest (1.17) at 50/spl deg/C/h, the slowest ramp rate.