Towards the real structure of quasicrystals and approximants by analysing diffuse scattering and deconvolving the Patterson

Methods based on X-ray area detectors are presented for acquiring and analy sing single-crystal X-ray diffraction data from quasicrystals and approxima nts. These methods are complementary to high-resolution diffractometry and fully exploit the possibilities of modern two-dimensional X-ray detector sy stems (imaging plates and charge coupled devices) such as the on-line read- out capability and the possibility to collect large volumes of reciprocal s pace in a quantitative and rapid way. Ln contrast to a classical point dete ctor, area detectors allow the measurement of a very large number of Bragg reflections in a reasonable time scale, as is shown with a large unit-cell periodic approximant in the Al-Co-Ni alloy system. For large approximants e xhibiting strong pseudosymmetry, direct methods for structure solution usua lly fail. Recently implemented Patterson deconvolution techniques are shown to succeed. The extension of techniques for area detectors - beyond the st andard application of collecting integrated Bragg intensities - to the quan titative acquisition of continuous and diffuse scattering data is presented with particular emphasis on quasicrystals. One of the key techniques is th e quantitative reconstruction of undistorted layers and volumes in reciproc al space. This is crucial for developing and comparing possible models for structural disorder in quasicrystals. Examples for decagonal Al-Co-Ni and i cosahedraI Al-Mn-Pd are given in respect to possibilities and limitations o f X-ray area detectors.