Abstract
High resolution transmission electron microscopy (HREM) at 400 kV has been used to image the oxygen sublattice in YBa 2Cu 3O 7− x ceramic superconductors observed during times short enough to avoid electron beam irradiation damage. HREM images along the a and b directions from very thin regions of the specimens observed at or near Scherzer defocus, resemble the projected potential maps of the structure: the Ba, Y, and Cu columns are seen as dark dots and the oxygen columns ar viewed as weak dark dots between the metal columns; whereas the oxygen vacancy are imaged as bright dots. Thus the [100] and [010] projections of the structure can be discriminated directly from the experimental HREM images. The dependence of the contrast of these images on dynamical scattering effects, Debye-Waller factor values and tilt misalignments in the microscopy has been studied through comparison between experimental and simulated images.
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