Partial Melt Processing of Solid-Solution Bi2Sr2CaCu2O8+delta Thick-Film Conductors with Nanophase Al2O3 Additions

Abstract : Partial-melt processing of BiSrCaCuO thick-film conductors with additions of nanophase Al2O3 was studied to increase flux pinning and inhibit SrCaCuO phase defect formation. Nanophase Al2O3 was added to Bi:Sr:Ca:Cu:O powders with four different compositions: three with Bi:Cu approximately 2:2 and one closer to the ideal Bi-2223 composition. The effect of Al2O3 addition on film microstructural and superconducting properties was studied for a range of partial-melt temperatures. Results were compared to Al2O3-free films with compositions lying within the single-phase solid-solution 2212 region. Nanophase Al2O3 reacted with 2212-type precursors to form a composite of micron size or smaller particles of solid-solution (Sr,Ca)3Al2O6 in a solid-solution 2212 superconducting matrix. The Ca content of the (Sr,Ca)3Al2O6 in a solid-solution 2212 superconducting matrix. The Ca content of the (Sr,Ca)3Al2O6 particles formed was approximately like 2212 precursor. Addition of 6-25% volume fraction of (Sr,Ca)3Al2O6 to Bi-2212 only slightly reduced Tcs and c-axis texturing, but improved film quality by reducing Sr-Ca-Cu-O defect volume fraction by factors of 2 to 6 and significantly increased Jc by over one order of magnitude for 0 to 2 T applied fields at 20 to 30 K.