MODE OF LEAD ADDITION AND ITS EFFECTS ON PHASE-FORMATION AND MICROSTRUCTURE DEVELOPMENT IN AG (BI,PB)(2)SR2CA2CU3OX COMPOSITE CONDUCTORS/

An extensive examination has been made of silver-sheathed (Bi, Pb)(2)S r2Ca2Cu3Ox (Bi-2223) composite conductors produced by the two-powder p rocessing method, wherein single-phase (Bi, Pb)(2)Sr2Ca1Cu2Oy (Bi-2212 ) is combined with a mix of Pb-Ca-Cu-O phases to give an overall stoic hiometry of Bi(1.8)Bb(0.4)Sr(2)Ca(2)Cu(3)O(x). The principal variable is the proportioning of lead between the Bi-2212 phase and the Pb-Ca-C u-O phases. X-ray diffraction measurements and scanning electron micro scopy analyses have revealed that the length of the induction period p rior to the onset of Bi-2223 formation decreases monotonically as the initial lead fraction in the Bi-2212 is increased up to a value of 0.3 . The observed decrease in critical current density of fully processed composites with decreasing lead fraction in the Bi-2212 phase appears to be more closely related to the quantity of unconverted Bi-2212 tha n to the quantity of residual alkaline earth cuprate secondary phases. Transmission electron microscopy shows that the frequency of Bi-2212 intergrowths declines with increasing lead fraction in the starting Bi -2212 component.