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 have been fabricated either from amorphous malic acid gels or via spray-drying of aqueous metal nitrate solutions. Calcination of the powders at 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-quality superconducting material. Identification methods for the superconducting and secondary phases by high-resolution optical microscopy employing normal and polarized light were developed. The texturing in the bulk samples and the effects of additional heat and mechanical treatments (by the powder-in-tube technique) on the microstructure were followed by optical microscopy. Fabrication techniques for tapes based on these observations yielded samples with critical current densities above 20 kA cm(-2).