X-Ray Diffraction Studies of Quasicrystals and Other Crystalline Materials

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w:\awards\awards96\*.doc 9625585 Colella Various x-ray diffraction experiments will be carried out on the icosahedral phase of Al-Pd-Mn. Since this alloy can be made into a quasicrystal with a high quality lattice structure, dynamical diffraction is feasible. The basic question still remains, "Where are the atoms?" and twelve years after the discovery of quasicrystals this question has not been fully answered. Experiments at Purdue and at the synchrotron light sources, NSLS and CHESS, will include quantitative studies of anomalous transmission (the Borrman effect), standing waves, and the use of circularly polarized x-rays. The basic issue of the centrosymmetry will be examined. An experiment will be carried out to determine the space group of the benzil molecular crystal that can be found in two enantiomorphic space groups and correlate optical activity with structure. %%% Various x-ray diffraction techniques, including experiments at the National Synchrotron Light Source and the Cornell High Energy Synchrotron Source, will be used to investigate the atomic arrangements in quasicrystals. These are new materials that do not exhibit long range periodicity as do most other solid substances. Their high strength, low density, low surface friction, and good oxidation resistance make them ideal for surface coatings. A company in France has set up a production line for using quasicrystalline coatings in frying pans instead of Teflon. Applications are envisaged for ball bearings, Some quasicrystals have exceptional qualities for hydrogen storage. ***