CRITICAL-CURRENT OF HIGHLY TEXTURED BI-2212 TAPES

Highly textured tapes, a few microns thick, of Bi 2212 high T-c superc onductor have been prepared by oxidation of metallic precursors electr olytically deposited onto polycrystalline silver ribbons. The microstr ucture of the specimens has been characterised by optical and scanning electron microscopy, X-ray diffraction and electron microprobe analys is. The resistive transition of optimized specimens was found to be ve ry sharp and to broaden very slowly with increasing current density. T -c has been always recorded with a current density of 500 A/cm(2). Cri tical current densities J(c) = 15 000 A/cm(2) have been measured at 77 K on specimens having an offset T-c = 82 K. These values correspond t o measurements performed with direct current. Magnetic measurements of J(c) as a function of temperature have been performed between 4 and 7 7 K, and the effect of magnetic fields // c, up to 6 tesla, on these c urrent densities has been determined. At 4 K and 0 tesla a J(c) = 10(6 ) A/cm(2) has been obtained and a current density as high as 3 10(5) A /cm(2) still remained at 6 tesla.