Exploring reciprocal space of a quasicrystal by means of an imaging plate

Abstract

A monochromatic Laue technique is used to extract information about the reciprocal lattice of a quasicrystal. A synchrotron beamline, normally available for protein crystallography, was used in this study. Each photograph is a planar projection of a spherical cap, a portion of the Ewald sphere, in reciprocal space. The algorithms needed to relate the images to reciprocal space are described in detail. It is found that many weak, but readily detectable, Bragg reflections are found in unexpected positions in reciprocal space, as predicted from theory. Some very weak Bragg reflections are clearly visible on the imaging plate, but could not be detected by photon counting using a four-circle diffractometer. Some images show characteristic `rings' or `arcs' of diffuse scattering, as previously observed in other icosahedral quasicrystals. In view of the `extreme perfection' of the quasicrystalline specimen used in this study, it is proposed to view these rings (or arcs) as intrinsic features of the icosahedral quasicrystalline structure.