DAFS and XAFS investigation of structural short-range order of decagonal Al-Co-Ni

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Due to the lack of long-range periodic order in quasicrystals there are restrictions concerning a straightforward structure analysis on base of x-ray diffraction data. Computed reflection intensities in x-ray diffraction patterns, which are strongly affected by the shape and occupation of hypothetical atomic surfaces, need to be compared with experimental data. The interatomic short-range correlations as to be determined by means of DAFS and XAFS have to be in agreement with these structural models. The use of linearly polarised x-rays allows for orientation sensitive determination of otherwise averaged short-range order information. Additionally wave vector-selectivity of DAFS can yield short-range order information sensitive to sites occupied by atomic species within the coherently scattering structural units.Structural models of decagonal Al-Co-Ni were applied to compute theoretical DAFS and XAFS functions. Calculation of both, energy-dependent structure factors and pair distribution functions obtained within a hypothetical cluster of app. 81 000 atoms as the basis of computation of DAFS are outlined.Co-K and Ni-K DAFS and XAFS measurements at 3 independent reflections of a decagonal Al70Co9.5Ni20.5 single crystal were performed and the experimental data were subjected to quantitative evaluation. The reflections used involved wave vectors parallel and perpendicular to the periodic direction and in a third inclined direction. In agreement with our simulations DAFS of individual reflections and thereby corresponding shortrange orders exhibited no differences within the error limits. The same was found for the case of polarized Co-K and Ni-K XAFS results.