The Atomic Structure Of The Zn-Mg-Rare-Earth Quasicrystals Studied By High-Resolution Electron Microscopy

Abstract

AbstractHigh-resolution transmission electron microscopy has been applied to study the real atomic structure of the decagonal (d-) quasicrystal in the Zn-Mg-rare-earth (RE) system, which is the first d-phase based on Frank-Kasper phase. We show that the phase has a novel structure in which the atomic arrangement in the tenfold symmetry plane can simply be interpreted as the Penrose tiling decorated by individual atoms - the simplest realization of the Penrose tiling as a real atomic structure. This is supported by the fact that a similar local atomic configuration exists in the Zn7Mg4crystal structure. This simple structural model is in sharp contras to the idea of atomic clusters, which has been successfully used to describe the structure of quasicrystals in Altransition metal alloys. The present results strongly suggest that the symmetric atomic clusters are not an essential factor for formation of quasicrystals. Instead, a new idea ofquasi-unit-celland itscoveringis applied for structural description. The atomic structure of the Zn-Mg-RE icosahedral phase is also implied to follow the present concept, based on the fact that its related crystalline phases with hexagonal lattices are not built of giant atomic clusters with icosahedral symmetry.