Inhomogeneities of composition, microstructure, and critical currents in elongated melt-textured YBCO samples

The microstructure, preferred orientation, and axial inhomogeneities of com position and critical currents in melt-textured YBCO samples in the shape o f bars were studied. The microstructure of the material is dominated by lar ge platelike grains. Most of these grains consist of YBa2Cu3Ox (123 phase); large grains of Y2BaCuO5 (211 phase) and a 123/211 intergrowth phase are a lso present. In addition, the material contains small, randomly oriented gr ains of Y2BaCuO5, YBa2Cu3Ox, and BaCuO2. A wide scatter in 211 content and oxygen stoichiometry of 123 along the bar samples is revealed. The variatio ns in phase composition are found to be strongly correlated with those in c ritical current.