MICRODEFECTS IN RELATIVELY FAST COOLING MTG YBCO SPECIMEN

We have carried out a microstructure analysis of an YBCO bulk sample p repared using a simplified version of the melt texture growth process. Using only a 200 kV transmission electron microscope and diamond knif e to section our sample, we obtain micrographs showing clear lattice f ringes with interference spacing around 13 angstrom. The boundaries of the bright and dark regions, which are believed to arise from variati ons in crystal composition, coincide with the occurrence of stacking f aults, twin boundaries and other dislocations. This sample, being full of microdefects, carries a bulk critical current of 1.75 x 10(4) A cm -2.