Intermetallic compounds with non-metallic properties

Intermetallic Compound Re2Ga9Ge with Re- and Ge-Embedded Gallium Clusters: Synthesis, Crystal Structure, Chemical Bonding, and Physical Properties

Transition metal-based endohedral cluster intermetallic compounds are interesting electron phases, which frequently exhibit superconductivity with a peculiar interplay between the critical temperature and valence electron count. We present a new Re-based endohedral gallium cluster compound, Re₂Ga₉Ge. Its unique crystal structure (P4₂/mmc space group, a = 8.0452(3) Å, c = 6.7132(2) Å) is built by two types of gallium polyhedra: monocapped Archimedean antiprisms centered by rhenium atoms and tetrahedra containing a main-group element inside. The analysis of chemical bonding shows the presence of localized pairwise interactions between the p-block elements and the formation of multicenter bonds with the participation of d-orbitals of rhenium. In the electronic band structure, the Fermi level is located in a narrow pseudogap indicating the optimum band filling and thus explaining the virtual absence of a homogeneity range. The compound exhibits Pauli paramagnetism and metallic properties with unexpectedly low thermal conductivity. A sharp anomaly observed on the magnetic susceptibility and resistivity curves presumably indicates the electronic phase transition accompanied by charge ordering at the characteristic temperature of T * = 271 K in zero magnetic field.

The Intermetallic Semiconductor ht-IrGa3: a Material in the in-Transformation State

The compound IrGa₃ was synthesized by direct reaction of the elements. It is formed as a high-temperature phase in the Ir-Ga system. Single-crystal X-ray diffraction analysis confirms the tetragonal symmetry (space group P4₂ /mnm, No. 136) with a = 6.4623(1) Å and c = 6.5688(2) Å and reveals strong disorder in the crystal structure, reflected in the huge values and anisotropy of the atomic displacement parameters. A model for the real crystal structure of ht-IrGa₃ is derived by the split-position approach from the single-crystal X-ray diffraction data and confirmed by an atomic-resolution transmission electron microscopy study. Temperature-dependent electrical resistivity measurements evidence semiconductor behavior with a band gap of 30 meV. A thermoelectric characterization was performed for ht-IrGa₃ and for the solid solution IrGa_3-x Zn _x .

Semiconducting and superconducting Mo–Ga frameworks: total energy and chemical bonding

The superconducting Mo₄Ga₂₁ structure type is derived from the electron-precise MoGa₄ cubic framework.