Current distribution and microstructure studies of isolated filamentsextracted from Ag-sheathed Bi(2223) tapes

Abstract

All the filaments extracted from an Ag-sheathed (Bi,Pb)2Sr2Ca2Cu3O10+x tape, prepared by theoxide-powder-in-tube technique, have been isolated by chemical etching of thesilver matrix, and individually characterized by keeping track of theirposition inside the conductor. Different types of measurements have beenperformed on each filament: magnetization hysteresis loops and zero-fieldcooled DC susceptibility by SQUID magnetometry; electrical resistivity by thefour-probe method; phase purity and texture by x-ray diffraction analysis; andstoichiometry by scanning electron microscopy/energy dispersive x-rayanalysis. The critical-current density jc of every filament has beencalculated from the magnetization hysteresis loops. At 77 K it has been foundthat the innermost filament carries a jc of 53 kA cm-2,i.e. much larger than for all the filaments of the outer shell (with jcranging between 25 and 40 kA cm-2). These results areconsistent with the variation in room temperature electrical resistivityobserved on the same samples. To some extent the observed current distributioncan be imputed to the different amount of cold working experienced by thefilaments. On the other hand, we have found that the average stoichiometry ofthe central filament matches well with that of the initial precursor powders,while in the filaments of the outer shell a consistent loss of Pb has beenobserved. The outer filaments also present a lower oxygencontent.