Phasonic disorder in decagonal Al-Co-Ni

Diffuse scattering from decagonal Al70Co12Ni18 (Edagawa phase) was investigated by means of Patterson methods. Basically two systems of diffuse intensities can be observed. The first system is found in quasiperiodic layers containing Bragg reflections. Model calculations show that underlying disorder can equally well be explained as phasonic disorder in a five dimensional approach, as well as fivefold orientational disorder of clusters in three dimensions. A second set of diffuse intensities is observed in layers halfway between the Bragg layers. Disorder associated thereto shows some correlation to phasonic/orientational disorder, but a different temperature dependency of the respective disorder phenomena suggests that these correlations are accidental.