B10M2 (M = Rh, Ir): finally a stable boron-based icosahedral cluster

The putative global minimum of clusters with formula B10M2 (M = Rh, Ir) corresponds to icosahedral structures formed by two alternately stacked B5 rings with the metals located at the top and bottom vertices.

Electrostatic potential in crystals of α-boron, γ-boron and boron carbide

An overview is given of the recently proposed method for computation of the electrostatic potential (ESP) of dynamic charge densities derived from multipole models [C. B. Hubschle, S. van Smaalen, J. Appl. Crystallogr. 2017, 50, 1627]. The dynamic ESP is presented for the multipole models of the boron polymorphs α-B12 and γ-B28, and stoichiometric boron carbide B13C2. Minimum values of the ESP are conspiciously equal at approximately −1 electron/Å. Regions with the ESP close to its minimum value form an extended network throughout the crystal structures at locations far away from atoms and bonds. Boron and boron carbide are extended solids containing an infinite network of strong chemical bonds. We have shown that for such solids, the ESP can usefully considered on Hirshfeld surfaces encompassing groups of atoms. Accordingly, we discuss bonding in boron and boron carbide with aid of the ESP on the Hirsfeld surface encompassing a B12 icosahedral cluster. The structure of the ESP corroborates the interpretation of the bonding characteristics previously proposed for α-B12, γ-B28 and B13C2.

Ferromagnetic transition in Au- based Approximants

The structure of Tsai-type magnetic quasicrystals and its related compounds (called approximants) are characterized by the space-filling of an icosahedral cluster which has a rare-earth icosahedron [1]. From an experimental point of view, such compounds have been known to show the spin glass like behavior without exception [2]. However, the discovery of the antiferromagnetic phase transition in the Cd-Tb approximant [3] gives a counterexample to this trend. Moreover, ferromagnetic transitions were observed in the Au-based approximant recently. In this paper, magnetic phase transitions in Au-Si-R (R= Gd ,Tb, Dy and Ho) approximants are discussed. In all the systems, the temperature dependence of magnetization show ferromagnetic transition at Tc. On the other hand, the magnetization curves below Tc are different between Gd-compound and non-Gd compounds. The difference in the magnetization may be attributed to the existence of the CEF effect in the non-Gd compounds which have non-zero orbital angular momentum.