Investigation of icosahedral phases in the Zn-Mg-(Y, Er) system by high resolution transmission electron microscopy

Icosahedral phases in Zn-Mg-RE(RE=Er, Y) alloys have been studied by high resolution transmission electron microscopy (HRTEM) and electron diffraction for different RE contents. From the electron diffraction patterns along the twofold axis, for Zn60Mg30+xY10−x a face centered icosahedral structure was found with x=0 whereas crystals with x in the range of 4 display a simple icosahedral structure. In the system with RE=Er a cubic approximant of the icosahedral quasicrystalline phase, the so-called ‘R-phase’, was found. The R-phase crystallizes in the space group F4̄3m with a0=2.02 nm. The close relation between the R-phase and the icosahedral quasicrystal is shown by HRTEM imaging.