Origin of J/sub c/ lateral spatial distribution in Ag-sheathed Bi-2212 HTSC tapes

Abstract

Critical current density (J/sub c/) spatial distribution in the superconducting core of the Ag-sheathed Bi-2212 tapes prepared by powder in tube technique has been measured by means of tape cutting along the rolling direction to a few narrow strips and separate J/sub c/ measurements each of them. The J/sub c/ value on the edges of tapes has been found to be higher by a factor of about 3 in comparison with the central area. Unexpectedly, the measured oxide core density is shown to be in contrary the lowest in the edge regions. The thin interface layer (about 10 /spl mu/m thick) with no secondary phase has been observed by SEM on the whole circumference of Ag-sheath/core boundary. This interface layer is assumed to be responsible for the dominant contribution to the supercurrent-carrying ability of a tape. However, in fact the J/sub c/-values on the very edge of the core still are twice as high as J/sub c/ in the central region (3.6/spl times/10/sup 4/ against 1.8/spl times/10/sup 4/ A/cm/sup 2/). Thus, an optimal structure formation can be promoted by the core edge geometry.