SINGLE-CRYSTAL X-RAY STUDY OF A MODULATED ICOSAHEDRAL ALCUFE PHASE

A single grain of a modulated icosahedral AlCuFe phase has been studie d by X-ray diffraction using the synchrotron light source at LURE (Lab oratoire pour l'Utilisation du Rayonnement Electromagnetique, Orsay, F rance), Each main icosahedral reflection is flanked by twelve satellit es along fivefold directions. The integrated intensity of 22 reflectio ns and of their satellites have been measured in a broad G(parallel-to ) and G(perpendicular-to) range. Despite the presence of the satellite s the overall icosahedral symmetry is maintained. The results are inte rpreted on the basis of six independent displacive cosine waves, propa gating along the fivefold axes of the 6-dim periodic space. The polari zation of these cosine waves is found to be longitudinal with a main c omponent in perpendicular space which means that the modulation is of <<phason>> origin.