STUDY OF THE LOCAL TRANSPORT AND STRUCTURAL PROPERTIES OF MULTIFILAMENTARY Ag-SHEATHED Bi(2223) TAPES

Abstract

It is known that the current flow in high quality Ag-heathed (Bi,Pb) 2 Sr 2 CaCu 3 O 10+x tapes shows a clear inhomogeneous behavior, as demonstrated by earlier magneto-optical experiments. In order to study this effect in detail we have extracted single filaments from a multifilamentary Ag-sheathed Bi(2223) tape, prepared by the Oxide-Powder-In-Tube technique. The filaments have been isolated by chemical etching of the silver matrix, and individually characterised according to their position inside the conductor. Different series of measurements have been performed on each filament: magnetisation hysteresis loops and zero field cooled DC susceptibility by SQUID magnetometry, electrical resistivity by the four-probe method, Bi(2223) phase purity and texture by XRD analysis, and local stoichiometry by SEM/EDX analysis. The microstructure analysis, in particular the study of the c-axis parameter and the microprobe analysis have revealed a higher Pb content (matching the starting stoichiometry) in the innermost filament. In addition to this result. It has been found by magnetisation measurements that the innermost filament carries a critical current density of 53 kA/cm 2 (at 77 K), i.e. a factor of two larger than for all the filaments of the outer shell (with j c ranging between 25 and 40 kA/cm 2). This result is in quantitative agreement with the room temperature electrical resistivity measurements performed on the same samples.