Einladung zum Promotionsvortrag von Frau Ella Schmidt:
„Disorder models from reciprocal space analysis in single crystal diffuse scattering“
Understanding the structure of materials is crucial for understanding their properties. Any deviation of perfect long-range order in a crystalline material will give rise to diffuse scattering in a diffraction experiment. This talk introduces a novel modulation wave approach to describe complex diffraction patterns and understand the underlying physical space ordering.
In modulated crystal structures, plane wave modulation functions vary the occupancy and/or displacement of atoms on certain sites within the crystal structure. These structures do no longer necessarily possess lattice periodicity in three-dimensional space. In (3+d)-dimensional superspace lattice periodicity can be recovered for modulated structures. This offers an elegant way to describe modulated structures and their diffraction patterns, including symmetry operations that give rise to extinction conditions.
Here, the disordered superspace approach will be presented. Disorder is introduced into superspace, breaking the (3+d)-dimensional lattice periodicity. This approach allows to describe structures that give rise to broad diffuse maxima, diffuse rods or planes in reciprocal space. Furthermore, the computational generation of disordered structures that show sharp satellite reflections on top of diffuse scattering is straight forward and the extinction conditions that are implied by the superspace symmetry are fulfilled.
The disordered superspace was developed for both occupational and displacement disorder. The sharp satellites on top of the diffuse planes observed in ThAsSe will be modelled as an application of the disordered superspace approach. (Vortrag auf Englisch)
Dem Vortrag schließt sich eine Diskussion von 15 Minuten an. Vortrag und Diskussion sind öffentlich. Diesen Verfahrensteilen folgt ein nicht öffentliches Rigorosum von 45 Minuten.