n-Beam lattice images. IV. Computed two-dimensional images

The contrast in electron-microscope lattice images of crystals oriented with a zone axis parallel to the incident electron beam has been computed for several complex oxides with large unit cells. The effects of changes in crystal thickness, image defocus, objective aperture size (up to 100 contributing diffracted beams) and spherical aberration are considered, and it is shown that, under certain conditions, the appearance of the image resembles that of the crystal structure. The bounds of applicability of the simple charge-density approximation are investigated.