High-resolution electron microscopy of the c=30.5 Å and c=38.2 Å polytypoids in the Bi-Ca-Sr-Cu-O superconductor

We report results of high-resolution structure imaging, image processing, and simulation of the c=30.5 Å (Tc =80 K) and c=38.2 Å (Tc =115 K) superconducting polytypoids in the Bi-Ca-Sr-Cu-O system. The increase in c parameter is due to the insertion of two layers of Cu-O perovskite+Ca atoms in each unit cell. From the processed image and simulations, it appears that the central Cu layer in the c=38.2 Å polytypoid may be oxygen deficient. In addition, the image simulation experiments suggest that the oxygen atoms in the Bi-O layers are located at the face center of the Bi lattice.