Distribution of critical current density in large YBa/sub 2/Cu/sub 3/O/sub 7-/spl delta// grains fabricated using seeded peritectic solidification

High quality large grain high T/sub c/ superconducting ceramics offer enormous potential as "permanent" magnets and in magnetic screening applications at 77 K. This requires sample dimensions /spl sim/cm with uniform high critical current densities of the order 10/sup 5/ A/cm/sup 2/ in applied magnetic fields of 1T. We report a study of the magnetic characterisation of a typical large YBa/sub 2/Cu/sub 3/O/sub 7-/spl delta// grain, prepared by seeded peritectic solidification, and correlate the magnetically determined critical current density, J/sub c/, with microstructural features from different regions of the bulk sample. From this data we extract the temperature, field and positional dependence of the critical current density of the samples and the irreversibility line. We find that whilst the bulk sample exhibits a good J/sub c/ of order 10/sup 4/ A/cm/sup 2/ (77 K, 1T), the local J/sub c/ is strongly correlated with the sample microstructure towards the edge of the sample and more severely at the centre of the sample by the presence of SmBa/sub 2/Cu/sub 3/O/sub 7-/spl delta// seed crystal.