Relationship between the microstructure and properties of PbO doped BISCCO 2223 superconductors synthesized from malic acid gels and from spray-dried nitrates

Abstract

Ceramic Pb_0.4Bi_1.8Ca_2.2Sr_2.0Cu₃O_y and Pb_0.3Bi_1.7Ca_2.4Sr_1.6Cu₃O_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 °C for 24 h and sintering of the compacted samples at 845 °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.