Is d-Al-Cu-Co a random tiling?

Channeling Monte Carlo simulations, in combination both with Rutherford bac kscattering (RBS) and pal-ride-induced X-ray emission (PIXE), have been per formed on model quasicrystals of decagonal Al-Cu-Co with different amount o f phason disorder. Comparing our simulation results to experimental data we obtain the best agreement For those models with a large amount of phason d isorder. This leads us to the conclusion that the sample of d-Al-Cu-Co used in the measurements is a random tiling. Besides the aspect of phason disor der we also examined the Cu and Co distribution given by the Burkov models (S.E. Burkov, Phys. Rev. B 47 (1993) 12325). We show that the chemical dist ribution is in contrast to the experimental PIXE yield profiles. By exchang ing some of the Cu and Co positions it is possible to eliminate the discrep ancy. (C) 2000 Elsevier Science B.V. All rights reserved.