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We have investigated the superconducting properties of bulk melt-processed YBCO using different experimental techniques. First, single domain materials (i.e. containing no grain boundaries) have been studied. Electrical resistivity, current-voltage characteristics, M-H loops, and A.C. susceptibility have been measured for different field and current directions. The intragranular properties are characteristic of high-quality melt-processed YBCO material, with a critical current density J/sub c/(T=77 K, B=1 T//c)>10/sup 4/ A/cm/sup 2/. The anisotropy ratio J/sub c/(ab)/J/sub c/(c) is found to be close to 3. Both magnetic and transport measurements show that defects in the microstructure do not significantly impede the current flow inside the single domain. These results were compared to those measured on samples containing one "natural" single grain boundary which sometimes appears during the grain growth process. The intergranular properties show a much stronger current and magnetic field dependence than that measured within the grain and these differences are discussed.
Date of Publication: June 1999