Two different superstructures of the decagonal Al-Co-Ni quasicrystal

The growth of decagonal Al–Co–Ni single crystals as a function of chemical composition

“…From low resolution SAED experiments, these satellites were interpreted to correspond to a twofold superstructure of the quasiperiodic phase. 9 Again, a high- resolution measurement is needed to find the correct assignment. By increasing further the Ni content (composition marked e in Fig.…”

“…10,11 The structure building elements, however, are not these layers but columnar clusters with ഠ20Å diameter and helical symmetry 10 5 ͞mmc that correspond to the ring contrasts observed by HRTEM. 3,4,9 It was observed that decagonal Al 70 Co 15 Ni 15 transforms during electron-beam irradiation in the electron microscope into two different quasiperiodic superstructures: one of them is characterized by the typical ഠ20Å ring contrasts, the other by ഠ 6Å circular patterns. 9 Despite the large amount of experimental work already done on the Al -Co-Ni system, many questions are yet to be answered: Does a perfectly ordered decagonal phase (without any diffuse scattering) exist, and in which compositional and temperature range is it stable?…”

“…Composition and temperature dependent investigations show a wealth of different diffraction phenomena like superstructure reflections and diffuse scattering corresponding to complicated structural ordering phenomena. [5][6][7][8][9] According to the first x-ray structure analyses on single crystals with nominal compositions Al 70 Co 20 Ni 10 and Al 70 Co 15 Ni 15 , respectively, the decagonal phase can geometrically be described by stacking quasiperiodic layers a and A (A denotes the layer a rotated around p͞5) with sequence . .…”

Indexing of Electron Diffraction Patterns of Icosahedral and Decagonal Phases

“…There are experimental observations of two separate classes of decagonal phases [32][33][34][35][36]. They are having space groups P10 5 /mcm and P10/mmm.…”

“…In contrast, quantification of zone rule for P10 5 /mcm types of structure requires a priori prescription of 16 (/) tt ratio. Thus the two Quasiperiodic structures having periodicity in one dimension of similar type [32][33][34][35] demand different types of hyperlattice parameters. This distinction has to be kept in mind while discussing these structures [9].…”