Diffraction Physics Studies on QuasicrystaÕs

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A variety of x-ray diffraction studies are proposed for improving our knowledge of the structures of quasicrystals. Multiple Bragg scattering will be used to measure phases of structure factors, and, in particular, to address the question whether or not certain quasicrystals have a center of inversion. It is proposed to measure intensity of Bragg reflection using synchrotron high energy x-rays, in order to circumvent the extinction and the absorption problems. Absolute measurements will be performed by measuring Compton scattering. The possibility for dynamical diffraction effects in quasicrystals will be explored. Standing waves experiments are proposed for the purpose of gaining some knowledge about the reciprocal positions in real space of the various atomic planes. The general purpose of the proposed research is to provide experimental information useful for a determination of the atomic sites in Al-Cu-Fe and Al-Pd-Mn quasicrystals. %%% Quasicrystals are metallic alloys that have many properties in common with ordinary crystals, yet their symmetry properties are not compatible with the laws of crystallography. The goal of this proposal is to determine the locations of the atomic sites. Besides their interest from the point of view of basic science, their exceptional resistance to oxidation, high temperature and alkaline corrosion makes then interesting as new materials.