STRUCTURAL CHARACTERISTICS AND ANISOTROPIC PINNING CENTERS OF MTG YBCO

The microstructure and defects in melt-textured growth (MTG) YBa2Cu3O7 -x (YBCO) bulk material have been studied systematically using high-re solution transmission electron microscopy (HREM), and the relationship between the anisotropic critical current density J(c) and the microst ructure have been explored. The results indicate that the well-texture d dense plate-shaped grains oriented parallel to the ab plane and the numerous intergrowth-type layered defects inside the plates are the tw o main structural characteristics in MTG YBCO. The former reduce weak links of grain boundaries, and the latter provide effective anisotropi c pinning centres. The intergrowth-type layered defects parallel to th e ab plane together with the well known {110} twin boundaries are resp onsible for the anisotropic behaviour of J(c), depending upon the orie ntation of the external magnetic field.