An X-Ray Diffraction and Electron Microscopic Study of a New High-Tc 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 Bi₄Ti₃O₁₂ 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=√2a _p, b=5√2a _p and c=8a _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.