The Co- -Ni distribution in decagonal Al 69.7(4) Co 10.0(4) Ni 20.3(4)

The Co- -Ni distribution in d-Al69.7(4)Co10.0(4)Ni20.3(4) was investigated based on X-ray and neutron diffraction data. The structure was modelled in higher dimensional space using the 'charge-flipping' and 'low-density elimination' methods and it was quantita- tively refined in three-dimensional space employing a pseudo-approximant approach. In higher-dimensional de- scription, the Co atoms are found at the centre of one of the two symmetry independent occupation domains, en- closed by regions mainly occupied by Ni. The other occu- pation domain is mostly occupied by Al. In physical space Co atoms are located in the centres of small Al pentagons and form pentagonal units, which are arranged in decago- nal rings. On these sites Co is partly substituted by Ni, while all other transition metal sites are occupied by Ni and to a minor degree by Al. The fraction of Co found on transition metal sites decreases with decreasing Co- -Co distances, whereby Co is replaced by Ni.