Investigation of superstructures in mullite by high resolution electron microscopy and electron diffraction

摘要: Superstructures in synthetic mullite, Al4+2xSi2−2xO10−x, prepared using the zone melting technique, are studied by high resolution electron microscopy (HREM), diffraction, and situ energy dispersive X-ray spectroscopy. For x=0.40 composition HREM images indicate only short-range order. Near x=0.5 mullite has an antiphase domain structure with boundaries (APB's) oriented parallel to (100). higher Al-content APB's run non-rational orientations which slightly inclined against {601}-planes. We propose models for superstructures oxygen vacancies arranged channels crystal b-axis. The supported a one-to-one match between observed computer-simulated images. An Al-rich limit of x=2/3 is deduced on basis stereochemical considerations. Different ordering schemes tetrahedral cations believed result orientation change near composition.