Electron microscopy
 
Decagonal Quasicrystal
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Decagonal structures are 2-D (two-dimensional) quasicrystals with 2-D quasiperiodic planes and a 1-D (one-dimensional) periodic axis along the 10-fold axis. Therefore, the decagonal quasicrystals are normally quasi-periodically packed columnar clusters that are periodic along the ten-fold axis with translation periods of ~0.4-3.6 nm and are atomically layered with flat or puckered atom layers in thickness of ~0.2 nm.

The main types of decagonal quasicrystal structures are Al-Fe-Pd, Al-TM (TM = Ir, Pd, Pt, Os, Ru, Rh, Mn, Fe, Co, Ni, Cr), Al-Ni-Co, Al-Cu-Mn, Al-Cu-Fe, Al-Cu-Ni, Al-Cu-Co, Al-Cu-Co-Si, Al-Mn-Pd, V-Ni-Si and Cr-Ni types. Table 1453 lists the structure details of some typical types of decagonal quasicrystals.

Table 1453. Structure details of some typical types of decagonal quasicrystals.

Decagonal type Phase example Stability Space group Remarks
Al-Co-Cu d-Co15Cu20Al65 (c = 0.4148 nm), Rh15Ni15Al70, d-Co15Ni15Al70 (c = 0.4081 nm) Stable P105/mmc Have a two-layer structure with a translation period (c) of ~0.4 nm
Al-Mn d-Mn16.5Pd13Al70.5 (c = 1.24 nm) Pd-stabilized P105/mmc Have a translational period (~1.2 nm) along the 10-fold axis.
Mn22Al78, Cu20Cr7Fe8Al65 Metastable  
Al-Fe-Pd T10Pd10Al80 (T = Fe, Ru, Os) Stable   Have a translational period (~1.6 nm) along the 10-fold axis.

For instance, Figure 1453a shows an electron diffraction pattern of a decagonal quasicrystal (space group: P105/mmc) with 0.4-nm periodicity along the 10-fold axis in an stable Al72Ni24Fe4 alloy that was solidified and then annealed at 850 °C for 50 h.

Electron diffraction pattern of an Al72Ni24Fe4 decagonal quasicrystal along its 10-fold axis

Figure 1453a. Electron diffraction pattern of an Al72Ni24Fe4 decagonal quasicrystal along its 10-fold axis. [1]

Both HAADF (high-angle annular dark-field) and ABF (annular bright-field) in a spherical aberration (Cs)-corrected STEM had been used to study the structure of an Al64Cu22Co14 decagonal quasicrystal (DQC) as shown in Figure 1453b. The bright dots in the HAADF-STEM image correspond to heavy atoms (z-contrast), while the projective positions of Al atoms, those of transition-metal (TM) Cu/Co atoms, and mixed sites (MSs) of Al and TM atoms in the ABF-STEM image are indicated by the dark dots. This alloy was prepared by annealing at 1173 K for 24 h, subsequently cooling down to 1073 K at a cooling rate of 2 K/h, keeping at 1073 K for 72 h, and finally quenching in water.

Al64Cu22Co14 decagonal quasicrystal

Figure 1453b. (a) HAADF-STEM image and (b) ABF-STEM image of an Al64Cu22Co14 decagonal quasicrystal (DQC). [2]

Figure 1453c shows electron diffraction patterns of the Al64Cu22Co14 DQC (in Figure 1453b) taken with the incident beam parallel to three primary axes. The diffraction patterns taken along directions q and p indicate that the structure includes two layers along the ten-fold axis and thus has centrosymmetry. The reflections marked by the arrows in Figure 1453c (c) disappear due to the existence of a 105 screw axis in the space group of P105/mmc.

Al64Cu22Co14 decagonal quasicrystal (DQC) diffraction

Figure 1453c. Electron diffraction patterns of the Al64Cu22Co14 DQC (space group: P105/mmc): (a) In ten-fold symmetry, (b) Along direction q and (b) Along direction p. [2]




 

 

 

 

 

[1] Hiraga, K., Yubuta, K., and Park, K.-T., High-resolution electron microscopy of Al-Ni-Fe decagonal quasicrystal. J. Mater. Res. 11, 1702, (1996).
[2] Kunio Yubuta, Kazuki Yamamoto, Akira Yasuhara and Kenji Hiraga, Structure of an AlCuCo Decagonal Quasicrystal Studied by Cs-Corrected STEM, Materials Transactions, 55(6), 866 (2014).

 

 

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