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

Channeling Monte Carlo simulations, in combination both with Rutherford backscattering (RBS) and pal-ride-induced X-ray emission (PIXE), have been performed on model quasicrystals of decagonal Al-Cu-Co with different amount of phason disorder. Comparing our simulation results to experimental data we obtain the best agreement For those models with a large amount of phason disorder. 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 disorder 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 distribution is in contrast to the experimental PIXE yield profiles. By exchanging some of the Cu and Co positions it is possible to eliminate the discrepancy. (C) 2000 Elsevier Science B.V. All rights reserved.