Highly perfect decagonal Al-Co-Ni quasicrystals

Conventionally solidified samples of decagonal Al70Co11Ni19 annealed at 1050 degrees C for 12 h, studied by electron diffraction and high-resolution transmission electron microscopy (HRTEM), display sharp spots in their diffraction patterns and almost no diffuse background scattering. Detailed geometric analysis of tilings constructed from rind superimposed onto HRTEM images show that the structure of these samples is very close to the perfect quasiperiodic structure of a Penrose pentagon tiling. This conclusion is corroborated by the observation that, for this structure, tilings in three sizes can be constructed using pattern matching based on semi(de)composition steps with a scaling factor tau. Moreover, these three tilings have a perpendicular space projection located in a window which is only very slightly-larger than the decagonal window of an ideal Penrose pentagon tiling.