Quasi-crystals and their crystalline homologues in the Al60Mn11Ni4 ternary alloy

Crystal structure of the Al20Mn5.37Ni1.31 phase in the Al–Mn–Ni system

The phase Al₂₀Mn_5.37Ni_1.31 in the ternary system Al–Mn–Ni system was synthesized by high-temperature sinter­ing and its crystal structure has been refined from single-crystal X-ray data.

The inter­metallic phase with composition Al₂₀Mn_5.37Ni_1.31 (icosa­aluminium penta­manganese nickel) was synthesized by high-temperature sinter­ing of a mixture with initial chemical composition Al₆₀Mn₇Ni₃. Al₂₀Mn_5.37Ni_1.31 adopts the Co₂Al₅ structure type in space-group type P6₃/mmc, replacing the Co atoms with the transition-metal atoms Mn and Ni. Structure analysis revealed that one of the two transition-metal sites is partially occupied by Ni [refined occupancy 0.342 (2)] and the other is co-occupied by Mn and Ni with a ratio of 0.895 (14):0.105 (14). The present refined chemical composition is supported by complementary energy-dispersive X-ray fluorescence (EDX) analysis and is in agreement with the previously determined Al–Mn–Ni phase diagram [Balanetskyy et al. (2011 ▸). J. Alloys Compd, 509, 3795–3805].

Multiple quasicrystal approximants with the same lattice parameters in Al-Cr-Fe-Si alloys

By means of atomic-resolution high-angle annular dark-field scanning transmission electron microscopy, we found three types of giant approximants of decagonal quasicrystal in Al-Cr-Fe-Si alloys, where each type contains several structural variants possessing the same lattice parameters but different crystal structures. The projected structures of these approximants along the pseudo-tenfold direction were described using substructural blocks. Furthermore, the structural relationship and the plane crystallographic groups in the (a, c) plan of these structural variants was also discussed. The diversity of quasicrystal approximants with the same lattice parameters was shown to be closely related to the variety of shield-like tiles and their tiling patterns.

X-ray and electron diffraction investigations on the stable decagonal phase in Co–Ni–Al alloys

The stable decagonal phase in alloys with compositions of Co15Ni15Al70, Co11.5Ni16Al72.5, Co16.5Ni11Al72.5 and Co20Ni7.5Al72.5 was investigated by X-ray and electron diffraction. All important projections of the reciprocal lattice of the decagonal phase were obtained by electron diffraction. The tilt angles between the individual zone axes were measured and compared with calculated angles. From the diffraction patterns the reciprocal lattice could be reconstructed. A simple method for the indexing of the reciprocal lattice is introduced. The indexing scheme is based on five linearly independent vectors. The indices for the reflections in the electron diffraction as well as the X-ray powder diffraction patterns are tabulated. The indices of the zone axes studied by electron diffraction could also be determined. In the X-ray diffraction studies a substantial variation of the number and of the position of the diffraction lines with alloy composition was found. The results are compared with results from the stable decagonal phase in the system Co–Cu–Al.