Quasicrystal element correlations from X-ray standing waves

Abstract

X-ray standing waves associated with dynamical diffraction in perfect crystals are also present during diffraction in high-quality quasicrystals. The fluorescence observed from quasicrystals while scanning the rocking curve of a particular Bragg reflection shows an identical form to that observed from periodic planes in a perfect crystal. In this case, however, the coherent fraction is the value of a correlation function: the Fourier component of a given elemental distribution at the wavevector associated with the Bragg peak. We show, using a model for Al−Pd−Mn, how the observed value for the coherent position at a given reflection is a sensitive indicator of the centrosymmetry of the distribution, and the observed value for the coherent fraction is a test of the elemental distribution predicted from the model.