VACANCY ORDERED PHASES AND ONE-DIMENSIONAL QUASI-PERIODICITY

The metastable vacancy ordered phases observed in aluminum-transition metal alloys on rapid solidification or vapor deposition can be considered as a periodic arrangement of a truncated quasiperiodic string based on the Fibonacci sequence along the 111 stacking direction of the original CsCl cell. Using the projection formalism developed in the context of quasicrystals, the diffraction patterns are calculated for commensurate and incommensurate projection from a periodic cubic cell in four dimensions. These are compared with experimentally observed patterns. It is suggested that there is a link between vacancy ordered phases and quasicrystals.