THE EFFECTS OF OXYGEN ON MELT-PROCESSING AG-SHEATHED BI2SR2CACU2O8 CONDUCTORS

The phase assemblages that form when Bi2Sr2CaCu2O8 (2212) incongruentl y melts have been studied as a function of temperature and partial pre ssure of O2 in the surrounding atmosphere. The critical phase assembla ge for melt processing is the one present when 2212 begins to form fro m the melt on cooling. Between 0.001 and 0.01 atm O2 the key phase in this assemblage is Bi2(Sr,Ca)3O3, from 0.075 to 0.30 atm O2 it is (Sr, Ca)CuO2, and from 0.40 to 1 atm O2 it is (Sr,Ca)14Cu24O(x). The range from 0.40 to 1 atm O2 is advantageous for melt processing as shown by the homogeneity of the microstructure of fully processed tape and the higher J(c) of tapes processed in 1 atm O2.