Hexagonal superstructures in the Zn-Mg-rare-earth alloys

We show that three types of hexagonal Zn-Mg-rare-earth (RE) ternary compoun d are formed in the vicinity of Zn6Mg3RE1. An electron diffraction study re vealed that these phases are related with a lattice parameters by a ratio 3 :5:7 but with approximately the same c parameters. A preliminary structural model for the phase with medium a parameter has been proposed by high-reso lution electron microscopy, based on the structures of the other two phases recently determined. It is shown that the two-dimensional hexagonal supers tructures can be described by two kinds of Zn-Mg clusters A and B, Linked b y RE atoms. (C) 1999 Elsevier Science S.A. All rights reserved.