Structural study of an Al73Ni22Fe5 decagonal quasicrystal by high-angle annular dark-field scanning transmission electron microscopy

Abstract

A water-quenched Al73Ni22Fe5 decagonal quasicrystal was investigated by the selected-area electron diffraction, convergent-beam electron diffraction and high-angle annular dark-field scanning transmission electron microscope methods. The alloy shows very sharp spots and nearly no diffuse scattering in the diffraction patterns, belongs to centrosymmetric space group P10(5)/mmc and is constructed almost by one type of 2 nm diameter atom cluster having mirror symmetry with a highly quasicrystalline order arrangement. Although a small number of 2 nm atom clusters having five-fold symmetry exists, which are similar to those observed in melt-quenched Al70Ni15Fe15, the structure of Al73Ni22Fe5 is considered to basically be the same as that of water-quenched Al72Ni20Co8, which is constructed only by mirror symmetry clusters arranged with a very high quasiperiodicity. The number of valence electrons per atom (e/a) of the present alloy (1.92) is very close to that of Al72Ni20Co8 (1.90), but differs from those of phases constructed by only the five-fold symmetry clusters. This implies that these alloys are Hume-Rothery electron compounds, whose structures are determined primarily by e/a value.

Structural disorder of the atom cluster in a highly-ordered decagonal quasicrystal of Al 72 Ni 20 Co 8

“…This indicates that the structural variation of the 2 nm cluster is not completely random but has an orientational order. This orientational order of the triangles is basically the same as the orientational order of the triangular arrangement of the cluster centres observed in the previous HAADF-STEM study [3,19].…”

Shock Synthesis of Decagonal Quasicrystals

“…It is noteworthy that the composition of the d-QC reported here is close to that of the thermodynamically stable decagonal phase in the Al-Ni-Fe system, Al 71 Ni 24 Fe 5 21 , which is known to exhibit the centrosymmetric P 10 5 / mmc structure 22 . The same results were found for the natural analogue of Al 71 Ni 24 Fe 5 , the mineral decagonite 5 , by single-crystal X-ray diffraction 6 .…”

New type of Al-based decagonal quasicrystal in Al60Cr20Fe10Si10 alloy

“…Generally, the strong diffraction spots from the nearby concentric circles in the tenfold EDP of DQCs can form pentagons (a green one is shown in Fig. 1a as an example), and consequently a series of pentagons with the ratio of edge lengths close to τ = 1.618 were generated if one links also the strong diffraction spots in the tenfold EDPs of other Al-based DQCs 25 38 . However, the two of five spots of the red pentagon (~τ times of the green one), as marked by small arrowheads, is much weaker than the other three strong spots in our case.…”

“…Two-dimensional (2D) decagonal quasicrystals (DQCs) have been attracted widely interest 1 2 3 4 5 6 7 8 9 10 11 since the discovery in the rapid solidified Al-Mn alloys by Bendersky 12 and in Al-Fe alloys by Fung et al 13 The DQCs were also achieved by slow solidification in the binary Al-Co alloys 14 and ternary Al-TMI-TMII systems (TMI, II: different transition metals) 4 . As one of crucial questions of the DQCs, the crystal structures of the ternary Al-Cu-Co 15 16 17 18 19 20 21 22 , Al-Ni-Co 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 , Al-Ni-Fe 38 39 , Al-Ni-Ru 40 , and Al-Mn-Pd 41 42 43 44 45 46 DQCs have been extensively studied by both X-ray diffraction and transmission electron microscopy (TEM), and the structural details of these DQCs have been revealed at an atomic scale. Although DQCs have also been found in the quaternary alloys, e.g.…”