COMBINATION OF HIGH-RESOLUTION ELECTRON IMAGING AND HOLOGRAPHY IN THEINVESTIGATION OF THE MODULATED STRUCTURE OF ZR4ON3F5

Thin crystals of Zr4ON3F5 were investigated by high-resolution electro n microscopy and holography in order to proof the value of electron ho lography to the investigation of complicated structures. The images re veal specific modulations of the basic fluorite structure and it was i nteresting what kind of information about the structure can be receive d from conventional imaging and from holography. The contrast of the h igh-resolution image in the ordered part of the crystal can be interpr eted and calculated from a fluorite-related superstructure with the b- axis four times that of fluorite. A second modulation of the structure along its c-axis, caused by a reaction under observation conditions i n the electron microscope and obvious not so regular like the modulati on from the superstructure, could not be explained from high-resolutio n images. This led us to record an electron hologram of such a region of the crystal and to investigate the structure using techniques stron gly related to electron holography. The image reconstruction from a hi gh-resolution electron hologram, using Fourier filtering to select onl y the fluorite beams, suggests that this second modulation is due to d islocations in the metal lattice, which create stacking faults in the structure.