Date Published: March 01, 2019
Publisher: International Union of Crystallography
Author(s): Philippe Scheid, Corentin Chatelier, Julian Ledieu, Vincent Fournée, Émilie Gaudry.
The physical significance of clusters in Al13TM4 compounds is invesitgated through ab initio methods based on density functional theory.
A large variety of intermetallic crystal structures are based on polyhedral entities, often called ‘clusters’, as first introduced by F. A. Cotton in the early 1960s to describe compounds containing metal–metal bonds (Cotton & Walton, 1982 ▸). This approach is very useful to represent the structures of complex intermetallic phases, like intermetallic clathrates, but also quasicrystals, their crystalline approximants and related phases (Steinhardt & Jeong, 1996 ▸; Suck et al., 2002 ▸; Abe et al., 2004 ▸). Typical clusters found in quasicrystals include the Mackay (Sugiyama et al., 1998 ▸), Bergman (Bergman et al., 1957 ▸) and Tsai clusters (Takakura et al., 2001 ▸), and numerous polyhedral shapes are used to describe complex intermetallics.
The bonding network in the Al13TM4 compounds is investigated in order to gain some insight into the various surface structures observed, the broken bond model being largely employed to account for surface energies (Ruvireta et al., 2017 ▸).
From the bonding analysis, the P-type in-plane bonding capacities are evaluated to be in the range 20–30%. The clusters are found to be rather stable entities, the intra-cluster Al–TMP-type interactions contributing 69–70% to the TMP-type bonding capabilities. In the following, we discuss the consistency of these results with the pseudo-tenfold surface structures identified so far.
We reported a systematic investigation of the electronic structure, phonon properties and chemical bonding network of bulk Al13TM4 compounds (TM = Co, Fe, Ru, Rh). Electronic structure calculations highlight rather strong hybridization. The strong TM–Al–TM bond within the Henley-type cluster leads to a strong anisotropy in the thermal displacement of the central Al atom. From the bonding analysis, the clusters are found to be rather stable entities, the intra-cluster Al–TMP-type interactions contributing 69–70% to the TMP-type bonding capabilities.