High Resolution Electron Microscopy of Crystal and Defect Structures of the High-Tc Superconductor Ba2YCu3O7-δ

Abstract
Structural study of the superconducting oxide Ba2YCu3O7-δ has been made at room temperature by high resolution electron microscopy. The orthorhombic structure was confirmed by the direct imaging of metal atoms. Planar defects with stacking sequence of metal-oxygen planes in the La2CuO4 type of structure were observed. Depending on the selected arca in electron diffraction, the axial ratio b/a was found to vary in a range from 1.003 to 1.018. Black and white contrasts appearing alternately along the twin boundaries are discussed in relation to the lattice distortion and the oxygen deficiency in the Cu-O layer.