Caged clusters in Al${}_{11}$Ir${}_4$: structural transition and insulating phase

Abstract

Using pair potentials fitted to an ab--initio database, combined with replica--exchange simulated annealing, we show the complex, quasicrystal-related Al${}_{11}$Ir${}_4$ compound contains a new version of the "pseudo-Mackay" icosahedral cluster, with non-icosahedral inner Al${}_{10}$Ir and/or Al${}_9$Ir clusters that exist in various orientations and account for partial occupancies in the reported structure. Two different compositions show first-order transitions to orientationally ordered phases doubling the (cubic) unit cell, which are respectively metallic and insulating.

arXiv comment5 pages and 3 figures

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