Structure of an Al-Fe-Ni decagonal quasicrystal studied by Cs-Corrected STEM

The structure of an Al-Fe-Ni decagonal quasicrystal with two quasiperiodic planes along the periodic axis in an Al₇₂Ni₂₄Fe ₄ alloy has been examined by spherical aberration (Cs)-corrected scanning transmission electron microscopy with high-angle annular dark-field and annular bright-field techniques. The transition-metal atoms and mixed sites (MSs) of Al and transition-metal atoms are represented as separated bright dots in the observed high-angle annular dark-field scanning transmission electron microscopy images, and consequently the arrangements of transition-metal atoms and mixed sites on the two quasiperiodic planes can be directly determined. The transition-metal atoms are arranged on a pentagonal tiling of an edge-length of 0.76 nm. The close examination of observed annular bright-field-and high-angle annular dark-field scanning transmission electron microscopy images indicates the existence of large decagonal columnar clusters with 3.2 nm diameter, and their arrangement on pentagonal, thin rhombic and squashed hexagonal tiles with an edge-length of 3.2 nm. The arrangements of transition-metal atoms in these three tiles are placed on an ideal pentagonal tiling with an edge-length of 3.2 nm, which is generated by the projection of a five-dimensional hyper-cubic lattice. The vertices are denoted by 5D hyper-cubic indices and then they are projected on the occupation domains in perpendicular space. The arrangement of Al atoms as well as transition-metal atoms and mixed sites in the large decagonal atom cluster with about 3.2 nm diameter is interpreted from the observed high-angle annular dark-field-and annular bright-field scanning transmission electron microscopy ABF-STEM images.