ARCS OF DIFFUSE-SCATTERING IN ICOSAHEDRAL GLASS MODELS

We report the results of experimental and simulation studies of the arcs of diffuse scattering in i-phase titanium quasicrystals and related phases. This work was undertaken to learn what kind of partial order in the samples produces the localized diffuse scattering. In particular, we investigate whether the experimental observations, arcs do not change with annealing and varying concentration, constrain any of the models that have been proposed. We have used the icosahedral glass (IG) model, which produces arcs in computed diffraction patterns, similar to those observed, by systematically varying the local structure in the manner of Robertson and Moss [Phys. Rev. Lett. 66 (1991) 353] to learn how the arcs of diffuse scattering are affected. An IG of point scatters produces diffraction peaks with non-zero width, arcs similar to those observed from real materials, and a broad background of diffuse scattering. Restricting a Site's local environment to contain only 'good' first neighbor distances sharpens both the peaks and the arcs, and increases their intensities relative to the broad diffuse background. Decoration of the IG by alpha(TiCrSi) clusters was examined. The localized diffuse scattering is intrinsic to the topological disorder of the random cluster packing; the effect of the atomic clusters was to modulate this intensity.