Effect of lead content on phase evolution and microstructural development in Ag-clad Bi-2223 composite conductors

摘要

A two powder process was used to prepare silver-sheathed monofilamentary Bi(sub 1.8)Pb(sub x)Sr(sub 1.98)Ca(sub 1.97)Cu(sub 3.08)O(sub y) (Bi-2223) tapes with varying lead contents, x, from 0.2 to 0.5. The resulting tapes were subjected to thermomechanical processing and then characterized by x-ray diffraction (XRD), scanning electron microscopy (SEM), and energy dispersive x-ray analysis (EDX). Layered phase texture was accessed using image analysis software on scanned SEM micrographs. Transport currents were measured at 77 K and zero field by the four-probe method. It was found that tapes with low lead content (X = 0.2 and 0.25) showed incomplete conversion to Bi-2223, had small grain size and poor c-axis texture. Tapes having higher lead content (x = 0.4 and 0.5) also showed incomplete conversion and the presence of lead-rich secondary phases. Tapes with lead content x = 0.3 and 0.35 showed complete conversion to Bi-2223, and had the least amount of secondary phases, the best c-axis texture, and the highest transport current (j(sub c)). The carbon content of the precursor powder also had a strong influence on secondary-phase chemistry.