Co-rich decagonal Al–Co–Ni: predicting structure, orientational order and puckering

Abstract

We apply systematic methods previously used by Mihalkovič et al. to predict the structure of the ‘basic' Co-rich modification of the decagonal Al₇₀Co₂₀Ni₁₀ layered quasicrystal, based on known lattice constants and previously calculated pair potentials. The modelling is based on Penrose tile decoration and uses Monte Carlo annealing to discover the dominant motifs, which are converted into rules for another level of description. The result is a network of edge-sharing large decagons on a binary tilling of edge 10.5 Å. A detailed analysis is given of the instability of a four-layer structure towards c doubling and puckering of the atoms out of the layers, which is applied to explain the (pentagonal) orientational order.

Acknowledgement

This work was supported by US Department of energy grant DE-FG02-89ER-45405.