The dislocations and twins in superconducting Bi-Ca-Sr-Cu-O samples are examined by scanning electron microscopy and transmission electron microscopy. The results indicate that these defects are inherent to the materials. The grains are large in size (1–10 μm), but they are frequently divided into subgrains by low-angle grain boundaries. Furthermore, evidence is found for discommensurate walls associated with incommensuration along the b axis.

• Received 8 September 1989

DOI:https://doi.org/10.1103/PhysRevB.41.4093