Origin of J(C) lateral spatial distribution in Ag-sheathed Bi-2212 HTSC tapes

Critical current density (J(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(c) measurements each of them. The 3, 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 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(c)-values on the very edge of the core still are twice as high as J(c) in the central region (3.6x10(4) against 1.8x10(4) A/cm(2)). Thus, an optimal structure formation can be promoted by the core edge geometry.