Modulated Structure of High-Tc Superconductor Bi-Ca-Sr-Cu-O Studied by High-Resolution Electron Microscopy and Electron Diffraction

Abstract
An incommensurate atomic displacive modulation has been clearly observed in high-resolution electron micrographs of the superconductive oxide Bi-Ca-Sr-Cu-O in addition to a concentration modulation in Bi layers. A commensurate form of the orthorhombic modulated structure has cell dimensions a=0.54, b=2.7 and c=3.08 nm. Characteristic features of electron diffraction patterns can be explained when transverse and longitudinal displacement waves for metal atoms along [010] are taken into consideration.