A cubic approximant in the Zn-Mg-Er alloy

A cubic approximant for the icosahedral phase is found in the Zn-Mg-Er syst em. The preparation of the Zn-Mg-Er ternary phase (the so-called R phase) t hrough quenching and annealing is described in detail. The R phase was foun d by means of scanning electron microscopy in combination with wavelength-d ispersive X-ray analysis. The composition of the R phase varies around Zn63 Mg23Er14 in different samples depending on the initial composition. The str ucture has been studied by a combination of high-resolution transmission el ectron microscopy (HRTEM) and X-ray powder diffraction. The R phase is cubi c with a(0) = 2.02 nm and crystallizes in the space group F (4) over bar 3m . The close relationship of this phase to the icosahedral phase in the Zn-M g-Y, RE system (RE = rare earth) is demonstrated through electron diffracti on features and HRTEM images.