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

Structural study of the superconducting oxide Ba 2 YCu 3 O 7-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 La 2 CuO 4 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.