PHASON-STRAIN ANALYSIS OF THE TWINNED APPROXIMANT TO THE DECAGONAL QUASI-CRYSTAL AL70CO15NI15 - EVIDENCE FOR A ONE-DIMENSIONAL QUASI-CRYSTAL

In high-resolution x-ray diffraction sometimes a pronounced splitting of the strongest Bragg reflections in decagonal Al70Co15Ni15 is observ ed. So far, this has been interpreted as evidence for a twinned (micro -)crystalline state with large lattice parameters. In the present pape r we show that the metrics can be perfectly reproduced by modeling a t winned one-dimensional quasicrystal rather than a twinned three-dimens ional crystalline phase. The split peak positions can easily be reprod uced by application of a linear phason strain on the ideal decagonal q uasicrystal and subsequent fivefold twinning. New high-resolution x-ra y-diffraction data are used in this analysis. An anisotropic broadenin g of all investigated reflections leads us to suggest a nonlinear phas on-strain component.