Seminars Archive

Investigation of defects in quasicrystals by using the new aspects of X-ray imaging connected to third generation synchrotron sources

Abstract
Defects in quasicrystals (QCs) remain a controversial topic. Previous electron microscopy investigations revealed the presence of defects similar to those observed in crystals. Nevertheless, in the case of QCs, they exhibit a complex associated strain field. For instance, dislocations have to be described in a higher dimensional space. This introduces, in the formulation of their related elastic displacement field, a new component with respect to the phonon one known for crystals, which is called phason strain field. Besides defects analogous to crystalline ones, we observed peculiar structural defects and inhomogeneities (dodecahedron shaped holes displaying discrete sizes and lamellar precipitates) in the volume of i-AlPdMn alloys investigated by using X-ray imaging techniques. We took advantage of the high spatial coherence properties of the X-ray beam produced by a third generation synchrotron radiation source. This allowed to use novel techniques, such as phase radiography and tomography, which have been combined in an original way with Bragg diffraction imaging. In particular, we could establish a link between structural defects and inhomogeneities. Different models will be presented in order to infer the origin of the various observed features. These results are shedding some light on the growth mechanism and structure stability in QCs.