High-resolution electron microscopy study of the early stage of formation of a Al-Pd-Mn decagonal quasicrystal from its crystalline approximant

Abstract

The formation process of the decagonal quasicrystalline phase (D-phase) with 1.2 nm periodicity from a crystalline approximant in the Al70Pd13Mn17 alloy has been identified by high-resolution electron microscopy. At the early formation stage, decagonal atom clusters, which are the most important structural units of the D-phase, were observed to segregate from the crystalline matrix with an atomic correlation determined by the structural characteristics of the crystal. A non-equilibrium structural state (a mixture of the segregated atom clusters and the crystalline matrix phase) was also observed, and its structural characteristics clearly revealed. The equilibrium D-phase, whose structure is characterized by an aperiodic arrangement of decagonal atom clusters with definite linkages and a long-range quasiperiodic correlation, was formed by fully annealing at 800degreeC for a long time. The linear phason strain in the equilibrium D-phase formed from the crystalline approximant may be related to the structur...