Substrate reactions and flux pinning structures in melt-processed YBa2Cu3O7 deposits on Ag-Pd alloy substrates

摘要

Results on melt-processing of thick deposits of highly homogeneous, submicron Y-123 powders prepared by aerosol pyrolysis on Ag-Pd alloy substrates are discussed. For long-term treatments at high temperatures, the extent of the substrate/deposit reaction increased with the Pd content of the substrate. At high Pd concentrations a Ba-Cu-Pd-O phase was formed, resulting in phase segregation of the deposit. For low Pd concentrations the only evidence of a reaction was the presence of a low density of copper oxide precipitates in the Ag-Pd substrate. TEM examination indicated that the substrate/deposit boundary was sharp, and no evidence of Pd contamination was found at 123/123 grain boundaries intersecting the substrate. The melt-processed deposits contain a very fine dispersion of 211 particles within the 123 phase. TEM examination has revealed the presence of a high density of stacking faults in the 123 near the 211/123 interfaces. Simple considerations suggest that these defects may be effective flux pinners for fields directed perpendicular to the basal plane.