Al-Ni-Co stable decagonal quasicrystals had been believed to belong to P105/mmc and to have decagonal symmetry of the basic atom-cluster column when projected along the decagonal axis. The space group and the projection symmetry of the cluster columns of Al70Ni30-xCox (x = 15 or 20) quasicrystals were re-examined by convergent-beam electron diffraction and high-resolution electron microscopy (HREM). It has been revealed that the space group is P105/mmc but the projection symmetry is pentagonal. The quasicrystals have been found to be isomorphic with Al-Cu-Co decagonal quasicrystals by Saitoh et al. in 1996 (Phil. Mag. A, 73, 381). The symmetries of the HREM image of the cluster column have been revealed to be pentagonal and decagonal at accelerating voltages of 200 and 300 kV respectively. The strong contribution of the 13420-type reflections at 300 kV smears the polar (pentagonal) image of the cluster column because electron waves scattered from all the atoms are superposed nearly in phase for the reflections with a lattice spacing of about 0-2 nm. It is demonstrated by computer simulations that a pentagonal atom-cluster-column model can produce pentagonal and decagonal HREM images at accelerating voltages of 200 and 300 kV respectively.
|ジャーナル||Philosophical Magazine A: Physics of Condensed Matter, Structure, Defects and Mechanical Properties|
|出版ステータス||Published - 1996 9|
ASJC Scopus subject areas