ELECTRON-MICROSCOPY OF NEAR-ICOSAHEDRAL STABLE AL-CU-LI QUASI-CRYSTALS

In order to clarify inconsistencies in previous electron microscopic and X-ray results on the structure of icosahedral Al-Cu-Li quasicrystals, a reinvestigation of this material has been made using selected area electron diffraction techniques, high resolution electron microscopy and image contrast calculations based on the models of Elswijk et al. and De Boissieu et al. A good fit for the first of these models and a somewhat less perfect fit for the latter in the projection normal to a two-fold axis are obtained. The high resolution micrographs show evidence for a contrast modulation with a 10 angstrom period normal to five-fold symmetry axes indicating a domain structure which may be connected with a chemical modulation.