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 Qper characteristic of a linear phason strain. Two other samples present a peak splitting proportional to Qper. Only two samples had their Bragg peak position corresponding to the ideal one, with a width increasing linearly with Qper. The perfection of one of these last two samples was investigated by synchrotron monochromatic X-ray topography. It was found to be a microstructure similar to the one exhibited by conventional crystals grown by the same technique (flux-growth).