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 sub per characteristic of a linear phason strain. Two other samples present a peak splitting proportional to Q sub per . Only two samples had their Bragg peak position corresponding to the ideal one, with a width increasing linearly with Q sub per . 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).