Comment on “Cleaved surface ofi-AlPdMnquasicrystals: Influence of the local temperature elevation at the crack tip on the fracture surface roughness”

Abstract

Quasicrystals are intermetallic compounds with long-range quasiperiodic translational order, composed of atomic clusters, which can be interpreted as basic geometric building blocks. It is a persistent discussion whether these clusters also represent physical entities. Cleavage planes of fractured icosahedral AlPdMn as well as sputtered surfaces annealed up to about 900 K are rough with clusterlike protrusions. Fivefold surfaces annealed at higher temperatures exhibit flat terraces. Thus, obviously, the clusters cannot be termed supermolecules. However, experiments and numerical simulations indicate that fracture is influenced by the clusters. Thus, they determine physical properties. In a recent paper, Ponson et al. [Phys. Rev. B 74, 184205 (2006)] investigated experimental fracture surfaces of AlPdMn and questioned the signature of the clusters. In this comment, we study the self-affinity of cleavage planes obtained by molecular-dynamics simulations. We conclude that the findings of Ponson et al. are not excluding a physical role of the clusters in quasicrystals.