HIGHLY PERFECT DECAGONAL AL-CO-NI QUASI-CRYSTALS

Conventionally solidified samples of decagonal Al70Co11Ni19 annealed a t 1050 degrees C for 12 h, studied by electron diffraction and high-re solution transmission electron microscopy (HRTEM), display sharp spots in their diffraction patterns and almost no diffuse background scatte ring. Detailed geometric analysis of tilings constructed from rind sup erimposed onto HRTEM images show that the structure of these samples i s very close to the perfect quasiperiodic structure of a Penrose penta gon tiling. This conclusion is corroborated by the observation that, f or this structure, tilings in three sizes can be constructed using pat tern matching based on semi(de)composition steps with a scaling factor tau. Moreover, these three tilings have a perpendicular space project ion located in a window which is only very slightly-larger than the de cagonal window of an ideal Penrose pentagon tiling.