Twins and Intergrowth Defects in High-Tc Bi-Sr-Ca-Cu-O Superconductor Examined by High-Resolution Electron Microscopy

Twinned structure with twin plane (510) and with the composition plane (001) is observed in a high- T c Bi-Sr-Ca-Cu-O superconductor which is orthorhombic with a =0.54, b =2.7 and c =3.08 nm. Directions of “Bi-concentrated bands” in both twin individuals are perpendicular to each other. Local intergrowths of perovskite-related layers with 1.8 and 2.1 nm thickness are observed among the major layers of 1.5 nm. The material includes small amounts of crystal with c =3.6 nm, which may be responsible for the superconductivity at 105 K, as already suggested by Muromachi et al. (Jpn. J. Appl. Phys. 27 (1988) L556).