An X-Ray Diffraction and Electron Microscopic Study of a New High-T_c Superconductor based on the Bi-Ca-Sr-Cu-O System

Abstract

Observed high-resolution images of a new high- T c superconductor based on the Bi-Ca-Sr-Cu-O system ( T c above 70 K) indicated a structure derived from the Bi 4 Ti 3 O 12 type in which doubled bismuth oxide layers alternate with double perovskite layers along the c -axis. The orthorhombic unit cell dimensions showed an approximate relation of a =√2 a p , b =5√2 a p and c =8 a p , where a p =3.82 Å, the cell parameter of a cubic perovskite. At least a quarter of the oxygen should be deleted in accordance with the average copper valence of less than 3 and two-dimensional Cu-O layers are supposed to be responsible for the high- T c superconductivity.