Structure of a Zn-Mg-Er cubic phase and its relation to icosahedral phases

The crystal structure of a cubic phase in the system Zn-Mg-Er has been solv ed by a combination of high-resolution electron microscopy and X-ray powder diffraction. This phase is considered to be related to that of the quasicr ystalline phase. The structure consists of 448 atoms in the unit cell with lattice constant of a(0) = 20.20 Angstrom and the space group is F<(4)over bar >3m. Important structural elements in the cubic structure are interpene trating icosahedral units around Zn and Mg atoms and Frank-Kasper polyhedra around the Mg atoms. No giant icosahedral atomic cluster, such as the 136- atom Bergman cluster, was found in the stucture.