RELATIONSHIP BETWEEN THE MICROSTRUCTURE AND PROPERTIES OF PBO-DOPED BISCCO-2223 SUPERCONDUCTORS SYNTHESIZED FROM MALIC-ACID GELS AND FROM SPRAY-DRIED NITRATES

Ceramic Pb0.4Bi1.8Ca2.2Sr2.0Cu3Oy and Pb0.3Bi1.7Ca2.4Sr(1.6)Cu(3)O(y) superconductors as precursor materials for bulk-phase applications hav e been fabricated either from amorphous malic acid gels or via spray-d rying of aqueous metal nitrate solutions. Calcination of the powders a t 800 degrees C for 24 h and sintering of the compacted samples at 845 degrees C for 100-150 h without intermediate grinding yielded high-qu ality superconducting material. Identification methods for the superco nducting and secondary phases by high-resolution optical microscopy em ploying normal and polarized light were developed. The texturing in th e bulk samples and the effects of additional heat and mechanical treat ments (by the powder-in-tube technique) on the microstructure were fol lowed by optical microscopy. Fabrication techniques for tapes based on these observations yielded samples with critical current densities ab ove 20 kA cm(-2).