Importance of bulk properties in the structure and evolution of cleavage surfaces of quasicrystals

The present work reviews the recent achievements in probing bulk properties of quasicrystals by using cleavage surfaces and surface sensitive techniques. In particular, it is shown that the cluster-subcluster-based structure of the cleavage surface of icosahedral Al-Pd-Mn quasicrystals can be related to the presence of stable atom clusters in the bulk, which force the crack front to circumvent them. Furthermore, by subjecting cleavage surfaces of differently pre-annealed Al-Pd-Mn quasicrystals to a post-cleavage heat treatment, we demonstrate that bulk vacancies migrate toward the surface, where they initiate structure and composition changes. These studies allow us to characterize Al-Pd-Mn quasicrystals with respect to their bulk vacancy concentration. As-grown Al-Pd-Mn quasicrystals are found to contain a supersaturation of all chemical species of vacancies in near stoichiometric composition, whereas long term pre-annealed material has a much lower, and predominantly Al, vacancy concentration. Analogous experiments for decagonal Al-Ni-Co quasicrystals show that as-grown Al-Ni-Co has a lower vacancy concentration than as-grown Al-Pd-Mn. (C) 2004 Elsevier Ltd. All rights reserved.