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Bil,7Pbo.3Sr2C~Cu3010 -y samples prepared by the glass precursor route were examined. A.c. susceptibility properties were studied and compared to those of samples obtained by the solid-state route, The interconnected lattice of 2223 needle-like grains in a matrix of strontium, calcium, and copper small and globular precipitates of irregular shape leads to an interesting behaviour of the critical current density as a function of d.c. field: there is high intergrain Jc and weak field dependence ( J , > lo5 A/cm2 at 77 K and 0 T), in contrast to Jc values and field dependence of classical solid-state route samples. It can thus be claimed (unambiguously now) that the intricate superconducting grain boundary structure acts as the ingredient for improved pinning at low d.c. field at least in such systems.

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