Cooling behavior of BSCCO/Ag tapes

The phase transformations taking place during cooling of BSCCO/Ag tapes have been investigated by means of high energy X-ray diffraction at a synchrotron source. This technique allows in-situ measurements of the concentration changes of the major structural phases, including liquids. In addition, information is obtained on stoichiometry and texture variations. Two mono-filament tapes were studied in air. The first tape was cooled at a constant rate of 50/spl deg/C/h. At temperatures above 730/spl deg/C the (Ca,Sr)/sub 2/CuO/sub 3/ and liquid phases are almost completely converted to 2212 and 2223. Below 780/spl deg/C a Pb-rich phase appears, either 3221 or (Ca,Sr)/sub 2/PbO/sub 4/. Simultaneously, shifts of X-ray lines indicate that 2223 is deprived of Pb, and from 730/spl deg/C onwards the concentration of 2223 drops. The second tape was cooled in steps to sequentially lower temperatures: 845/spl deg/C, 820/spl deg/C and 660/spl deg/C. At the former two steps (Ca,Sr)/sub 2/CuO/sub 3/ and liquid phases are again converted to 2212 and 2223, while at 660/spl deg/C they are rapidly converted to 2212 and-primarily-2201. Also at 660/spl deg/C, 2223 decomposes to 3221 or (Ca,Sr)/sub 2/PbO/sub 4/ at a rate of 40% per hour.