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

TL;DR

This study investigates the structural and electronic properties of Al$_{11}$Ir$_4$, revealing a new cluster type, phase transitions, and differing electronic behaviors in ordered phases, using computational modeling and simulated annealing.

Contribution

It introduces a new version of the pseudo-Mackay icosahedral cluster in Al$_{11}$Ir$_4$ and details the structural transitions and electronic phases based on computational analysis.

Findings

Discovery of a new cluster type in Al$_{11}$Ir$_4$

Identification of first-order phase transitions

Different electronic properties in ordered phases

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.