The interest of x-ray imaging for the study of defects in real quasicrystals

The understanding of defects in quasicrystals has improved through x-ray im aging at ESRF, one of the first operating third-generation synchrotron radi ation sources. These sources, while enhancing the possibilities of x-ray to pography, opened the way to new techniques like phase contrast radiography and tomography. The combination of these techniques makes it possible to vi sualize and characterize both structural defects and inhomogeneities in the bulk of real quasicrystals. Defects exhibiting a loop-shaped contrast, pre viously observed by x-ray topography in both AlCuFe and AlPdMn quasicrystal s, were related to inhomogeneities (holes and precipitates) revealed by pha se radiography and tomography. The evolution of the defects after annealing provides clues on their nature and formation. The experimental results are discussed with reference to the existing structural models for quasicrysta ls. Those concerning holes are in fair agreement with the predictions of a theoretical model introduced by Janot et al to describe the structure of ic osahedral AlPdMn quasicrystals in terms of hierarchical self-similar packin g of overlapping atomic clusters.