CRITICAL CURRENTS AND MICROSTRUCTURE OF MELT-TEXTURED STOICHIOMETRIC YBA2CU3O7-DELTA CRYSTALLITES

To avoid weak-link behavior caused by grain boundaries small crystallites of YBa2Cu3O7-delta were mechanically separated from approximately 1 cm3 Bridgman-melt-textured blocks. Using the Bean critical-state model, j(c) values at 4 K and 5 T (70 K and 2 T) as high as approximately 2 X 10(6) A/cm2 (approximately 4 X 10(4) A/cm2) were estimated from the width of the magnetization hysteresis. Microstructural investigations of the crystallites reveal the existence of dislocations, finely distributed inclusions, stacking faults, twin boundaries, elementary growth steps, and oxygen-deficient regions. The defects are thought to have a strong influence on the pinning behavior and the shape of the magnetization curve.