Kupsch, A.; Meyer, D. C.; Gille, Peter; Paufler, P.
DAFS and XAFS investigation of structural short-range order of decagonal Al-Co-Ni.
In: Physica Scripta, Vol. T115: S. 255-260
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Due to the lack of long-range periodic order in quasicrystals there arerestrictions concerning a straightforward structure analysis on base ofX-ray diffraction data. Computed reflection intensities in X-raydiffraction patterns, which are strongly affected by the shape andoccupation of hypothetical atomic surfaces, need to be compared withexperimental data. The interatomic short-range correlations as to bedetermined by means of DAFS and XAFS have to be in agreement with thesestructural models. The use of linearly polarised X-rays allows fororientation sensitive determination of otherwise averaged short-rangeorder information. Additionally wave vector-selectivity of DAFS canyield short-range order information sensitive to sites occupied byatomic species within the coherently scattering structural units.Structural models of decagonal Al-Co-Ni were applied to computetheoretical DAFS and XAFS functions. Calculation of both,energy-dependent structure factors and pair distribution functionsobtained within a hypothetical cluster of app. 81 000 atoms as the basisof computation of DAFS are outlined.Co-K and Ni-K DAFS and XAFS measurements at 3 independent reflections ofa decagonal Al70Co9.5Ni20.5 single crystal were performed and theexperimental data were subjected to quantitative evaluation. Thereflections used involved wave vectors parallel and perpendicular to theperiodic direction and in a third inclined direction. In agreement withour simulations DAFS of individual reflections and thereby correspondingshort-range orders exhibited no differences within the error limits. Thesame was found for the case of polarized Co-K and Ni-K XAFS results.