PERIODIC SUPERORDER AND DISORDER OF DECAGONAL AL-NI-CO AND AL-CO-CU(-SI) PHASES

Commensurate satellite reflections in diffraction patterns of decagona l Al-Ni-Co and Al-Cu-Co phases indicate a periodic superorder on the q uasiperiodic substructure. From the intensity characteristics of these satellites a box-like modulation function is derived which may be vis ualized in different ways including approximant phases. An interpretat ion by fine-scale periodic lamella microdomains matches closely high-r esolution electron microscopy observations and characteristic structur al features of the average structure.