From phason planes to superstructures in an Al–Pd–Mn alloy

Abstract

The atomic structures of four structurally complex phases of an Al–Pd–Mn alloy, namely the Ψ-, ξ1-, ξ2- and ξ3-phases, have been determined by means of high-resolution electron microscopy and by theoretical structure simulations based on the periodic stacking of two different types of phason planes. The structural characteristics of the Ψ-phase appears as a thin slab of ξ′-phase sandwiched between a pair of type-1 phason planes; in addition, three newly-found ξ i -phases (i = 1–3) were constructed by periodic stacking of the type-2 phason planes with an adjacent stacking (ξ1), centred by a flattened hexagon (ξ2), which are sandwiched around a thin slab of ξ-phase (ξ3). High-resolution electron microscopy image simulations of the Ψ-phase based on our structural model match very well with the experimental results and this agreement is also supported by electron diffraction and X-ray powder diffraction simulations based on the model. Our results show that structural models of periodic stacking of two types of phason planes can be used to construct the atomic structure of ξ′- and ξ-phase related superstructures in the Al–Pd–Mn alloy.