DAFS and XAFS investigation of structural short-range order of decagonal Al-Co-Ni
Physica Scripta T115: 255-260
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 short-range orders exhibited no differences within the error limits. The same was found for the case of polarized Co-K and Ni-K XAFS results.