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 re¯ections are found in unexpected positions in reciprocal space, as predicted from theory. Some very weak Bragg re¯ections 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.

X-ray diffuse scattering in the icosahedral quasicrystal Al-Pd-Mn

“…In a separate experiment, described in Ref. 6, we took diffuse scattering data using a technique called the ''monochromatic Laue method.'' This method simply consists of keeping a crystal stationary on a monochromatic x-ray beam, and recording the diffraction pattern on a flat film, ͑in our case, an imaging plate͒ perpendicular to the incident beam, placed downstream with respect to the crystal.…”

“…The sample was the same as that used in a separate diffuse scattering experiment in which use was made of an imaging plate as a detector. 6 A detailed description of the specimen was given in Ref. 6, and it is partially reproduced here.…”

“…6 A detailed description of the specimen was given in Ref. 6, and it is partially reproduced here. The sample was a thin slice of Al 71.0 Pd 20.5 Mn 8.5 cut perpendicular to a twofold axis ͑within 0.25°), and diamond polished on both sides.…”

Towards the real structure of quasicrystals and approximants by analysing diffuse scattering and deconvolving the Patterson

“…This technique was used in a recent study on icosahedral Al± ±Mn± ±Pd (Kopecky, Colella, 1999) but is only of limited value for structural studies. Since a spherical shell of reciprocal space intersecting the Ewald sphere is projected onto the flat area detector, only a distorted image of the reciprocal space is obtained.…”