Dynamical Three -Beam Diffraction in a Quasicrystal
نویسنده
چکیده
Multiple Bragg scattering is a source of phase information. A quantity 8 called the triplet invariant can be determined: 8 = ~u + q~r-n q~v, where q~n is the phase of the simultaneous reflection H, P is the main reflection, and P [] is the coupling reflection. Previous experiments on A1-Pd-Mn have always yielded 8 values far from 0 or 180 °, the only values compatible with a centrosymmetric structure. In this work, a new approach is used. Instead of concentrating on the wings of the azimuthal plots, the central region is considered where the H reflection is fully excited. Circularly polarized X-rays are also used. The difference in the azimuthal plots between left and right polarization is a source of phase information. This approach is feasible with AI-Pd-Mn because the crystal perfection of this material is outstanding and dynamical theory can be applied to all regions of the azimuthal plot. A noticeable difference in the azimuthal plots is visible when the helicity is switched. N-beam dynamical theory without approximations is used to fit theoretical profiles to the experimental azimuthal plots. In all cases, a triplet invariant 3 = 50 + 10 ° was found. It is confirmed that AI-Pd-Mn is not centrosymmetric.
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