HIGH-QUALITY BI-2212 TAPES PREPARED BY OXIDATION OF METALLIC PRECURSORS

Aiming at manufacturing long lengths of Bi-2212 tapes, we have develop ed a technique of synthesis by oxidation of metallic precursors. This technique is based on the sequential electrodeposition of the constitu ting metals (Cu, Bi, Ca and Sr) onto polycrystalline silver tapes, fol lowed by oxidation at temperatures in the interval 800-880 degrees C. The deposition sequence as well as the thermal treatments have been op timized using the results of a complete microstructural characterisati on made by optical and scanning electron microscopy, X-ray diffraction , electron probe microanalysis as well as DTA and TGA analysis. As a r esult, highly textured tapes, a few microns thick, have been obtained. The resistive transition of the optimized specimens is quite sharp, o f the order of 2 K, measured with a direct current density of 500 A/cm (2). Transport critical current densities J(c) = 15,000 A/cm(2) have b een obtained at 77 K on specimens with a T-c(offset) = 82 K. From magn etic measurements (Bean model) a J(c) of 10(6) A/cm(2) has been found at 4 K.