High-resolution transmission electron microscopy of the Al‒Pd‒Mn decagonal quasicrystal with 1.6 nm periodicity and its crystalline approximants

Abstract

The structural characteristics of the decagonal quasicrystal with 1–6 nm periodicity and its various crystalline approximants in the Al₇₀Pd₂₀Mn₅ system have been revealed by high-resolution electron microscopy. It is shown that the Al‒Pd‒Mn decagonal quasicrystal, formed as a main phase by rapid solidification, contains a kind of atom column with about 1.6 nm periodicity as the most fundamental structural unit. The two-dimensional aperiodic arrangements of the atom columns with definite linkages constructs the main structure of the decagonal quasicrystal. The quasiperiodic structural characteristic of the Al‒Pd‒Mn decagonal quasicrystal with 1.6 nm periodicity is compared with that of a Penrose tiling and that of an Al‒Pd‒Mn decagonal quasicrystal with 1.2 nm periodicity. Various crystalline approximants of the decagonal quasicrystal with 1.6 nm periodicity, existing in the as-casted and annealed states, are presented. It is shown that their structures can be systematically understood as various periodic arrangements of the same kind of atom column as those in the decagonal quasicrystal with the same type of linkage. The close structural relationships among these structures have been directly revealed by observation of their intergrowth.