EFFECTS OF MICROSTRUCTURE AND SECONDARY PHASES ON THE SUPERCONDUCTING PROPERTIES OF AgAu SHEATHED BI-2223 TAPES

摘要

For the purpose of investigating the effects of secondary phases and microstructure on the superconducting properties of Bi-2223 tapes, AgAu sheathed monofilamentary tapes with nominal composition Bi_(1.84)Pb_(0.34)Sr_(1.91)Ca_(2.03)Cu_(3.06)O_x were chosen for the present study. Secondary phases were examined with x-ray diffraction and scanning electron microscopy at different stages during the process of Bi-2223 formation. CuO, (Ca,Cu)_xO_y, Ca_2PbO_4 and (Bi,Sr) rich phases were found to be the secondary phases in the Bi-2223 tapes throughout the whole process. Current-voltage characteristics of the tapes were measured with a standard four probe method at 77K in zero magnetic field. In addition, the irreversibility line was obtained from magnetization measurements and J_c as a function of temperature estimated from the remanent magnetization. These measurements imply that the current pathways in these materials, that are the product of a sequence of heating and intermediate deformations, are complex.