Structural Characteristics of Al-Co-Ni Decagonal Quasicrystals and Crystalline Approximants

The Structure of an Al–Co–Ni Decagonal Quasicrystal in an Al₇₂Co₈Ni₂₀ Alloy Studied by Cs-Corrected Scanning Transmission Electron Microscopy

“…1. The clusters with a pentagonal arrangement of bright dots, which are rarely observed in this decagonal quasicrystal, are common ones in the other AlCoNi decagonal quasicrystals, 6,7) whereas the clusters with decagonal and asymmetric arrangements of bright dots are ones appearing in this decagonal quasicrystal. 8) Figure 2(a) is an ABF-STEM image of the Ni-rich decagonal quasicrystal.…”

“…The structures of five types of AlNiCo decagonal quasicrystals except for one referred to as Ni-rich basic structure (hereafter called as Ni-rich decagonal quasicrystal) have been interpreted by BOO arrangements of columnar atom clusters with a decagonal section of 2 nm in diameter. 6,7) On the other hand, the Ni-rich decagonal quasicrystal and AlNiFe one, which are known to be ones of highly ordered quasicrystals, were characterized by an arrangement of columnar atom clusters with 3.2 (= 2 ©¸) nm in diameter. 8,9) However, the recent investigation of the Ni-rich decagonal quasicrystal with Cscorrected STEM, which has an enough resolution to represent individual TM atoms as separated bright dots in observed images of decagonal quasicrystals, has discussed the structure of only the 2 nm atom cluster, and has never touched on the 3.2 nm cluster.…”

Arrangements of Transition-Metal Atoms in Three Types of Al–Co–Ni Decagonal Quasicrystals Studied by Cs-Corrected HAADF-STEM

“…6,7) The structures of five types of the AlNiCo decagonal quasicrystals, except for one referred to as Ni-rich basic structure, can be characterized by ordered arrangements of two types of the clusters with different orientations of pentagonal symmetry, and can be divided into two groups, e.g. structures formed with arrangements of one type of clusters with the same orientations and those of ordered arrangements of the two types of the clusters with different orientations.…”

“…The three decagonal quasicrystals can be understood as structures of two quasiperiodic planes with a period of 0.4 nm along the periodic axis, if weak diffuse reflections showing a period of 0.8 nm are neglected. 6) Therefore, the structures of the decagonal quasicrystals are characterized by arrangements of TM atoms and MSs in the two quasiperiodic planes. 12.5 ingots were sealed in evacuated quartz tubes, annealed at 900°C for 120 h, at 1000°C for 65 h and 900°C for 72 h, respectively, and then quenched in water.…”

“…structures formed with arrangements of one type of clusters with the same orientations and those of ordered arrangements of the two types of the clusters with different orientations. 6,7) Recent Cs-corrected STEM has an enough resolution to represent individual TM atoms as separated bright dots in observed images of decagonal quasicrystals. 8,9) Therefore, in the present paper, we intended to reexamine the structures of the AlCoNi decagonal quasicrystals by Cs-corrected HAADF-STEM observations.…”