Evaluation of high-resolution electron microscopy as a method for studying Y-Ba-Cu-O superconductors

High-resolution transmission electron microscopes operating at 300 and 400 kV were used to investigate the crystallography and microstructure of the perovskitelike YBa2Cu3O7-x. In this paper, we evaluate the performance attainable with these microscopes both empirically and by computer modelling. Based upon the assumption that oxygen may be a key to superconductivity properties, we have also investigated the visibility of the oxygen sites as well as the heavier yttrium and barium ion positions and the lighter Cu atom positions. We propose a scheme for observing different twin orientations in these structures and hence the oxygen atom positions seen in projection for the [100] and [010]. Our observations of both thick and thin regions of Y-Ba-Cu-O materials are reported as well as the problems of adjusting microscope parameters and specimen alignment to obtain interpretable images. We also give a preliminary report on the effects of heat treatment as seen in high-resolution micrographs to assess disorder of the heavy atoms and oxygen vacancies.