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

To avoid weak-link behavior caused by grain boundaries small crystalli tes of YBa2Cu3O7-delta were mechanically separated from approximately 1 cm3 Bridgman-melt-textured blocks. Using the Bean critical-state mod el, 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 t he width of the magnetization hysteresis. Microstructural investigatio ns of the crystallites reveal the existence of dislocations, finely di stributed inclusions, stacking faults, twin boundaries, elementary gro wth steps, and oxygen-deficient regions. The defects are thought to ha ve a strong influence on the pinning behavior and the shape of the mag netization curve.