Phason strain and structural perfection in the Zn-Mg-rare-earth icosahedral phases

The structural perfection of eight samples of icosahedral Zn-Mg-R (R=Y, Ho and Tb) single grains has been studied by high resolution X-ray diffraction , Four samples present a systematic peak shift proportional to Q(per) chara cteristic of a linear phason strain. Two other samples present a peak split ting proportional to Q(per). Only two samples had their Bragg peak position corresponding to the ideal one, with a width increasing linearly with Q(pe r). The perfection of one of these last two samples was investigated by syn chrotron monochromatic X-ray topography. It was found to be a microstructur e similar to the one exhibited by conventional crystals grown by the same t echnique (flux-growth). (C) 2000 Elsevier Science B.V. All rights reserved.