Diffraction Physics Studies on QuasicrystaÕs

提出了各种x射线衍射研究，以提高我们对准晶体结构的认识。多次布拉格散射将用于测量相的结构因素，特别是，解决是否某些准晶体有反转中心的问题。为了克服消光和吸收问题，提出了利用同步加速器高能x射线测量布拉格反射强度的方法。绝对测量将通过测量康普顿散射来进行。将探讨准晶体中动态衍射效应的可能性。提出了驻波实验，目的是获得关于各种原子面在实空间中的互易位置的一些知识。所提出的研究的一般目的是为确定Al-Cu-Fe和Al-Pd-Mn准晶体中的原子位置提供有用的实验信息。准晶是一种金属合金，它具有许多与普通晶体相同的性质，但它们的对称性与晶体学定律不相容。这项建议的目标是确定原子场址的位置。除了从基础科学的角度来看，它们的特殊抗氧化性、高温性和碱性腐蚀性使它们作为新材料变得有趣。

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.