IMAGING OF CU AND O VACANCIES IN (BI,PB)2SR2CA2CU3O10 BY HIGH-RESOLUTION TEM

High-resolution transmission electron microscopy was used to image copper and oxygen vacancies in high-T(c) (Bi,Pb)2Sr2Ca2Cu3-xOz (n = 3 phase) superconductors. The n = 3 phase containing the Cu and oxygen vacancies was observed at grain boundaries and was only a few lattice parameters thick. High-resolution image simulation showed that the appearance of bright lines at the position of the central CuO layer, which was the experimental evidence for the presence of vacancies, cannot be explained by oxygen vacancies alone but also requires Cu vacancies. This new type of defect is a point defect which is restricted to a specific crystallographic plane. It documents the difference in bonding between the central and the outer CuO layers. The possibility of creating Cu and O vacancies in the central CuO layer seems to offer a possibility for fine tuning the electrical properties of this material.