1. Bonding concepts and structure-property relationships of ICs

Bonding in metallic systems is not easily facilitated. Structural stability of ICs and alloys is often governed by a delicate interplay between electrostatic and electronic contributions to the total energy. This in turn gives metallic and covalent components to chemical bonding. We investigated the metal-nonmetal border within the periodic table, where the group 12 (Zn-group) and group 13 elements (boron group) are located. The structures of these elements display striking deviations from the simple packings fcc, hcp, and bcc usually observed for elemental metals. As a result, we could develop a unified bonding principle for those elements, which explains the unusual ground state structures and even accounts for high-pressure structural transitions.

A. S. Mikhaylushkin, S. I. Simak, B. Johansson, U. Häussermann ”Electron Concentration and Pressure Induced Structural Changes in Alloys In 1-xX x (X = Cd, Sn)” Phys. Rev. B, 72 (2005), 134202.

A. S. Mikaylushkin, U. Häussermann, B. Johansson, S. I. Simak “Fluctuating Lattice Constants in Indium under High-Pressure” Phys. Rev. Lett., 92 (2004), 195501.

U. Häussermann, S. I. Simak “Origin of the c/a Variation in Hexagonal Close-Packed Divalent Metals, Phys. Rev. B, 64 (2001), 245114.

S. I. Simak, U. Häussermann, R. Ahuja, S. Lidin, B. Johansson ”Gallium and Indium under High Pressure, Phys. Rev. Lett., 85 (2000), 142.

U. Häussermann, S. I. Simak, R. Ahuja, B. Johansson ”A Unified Bonding Picture for the Metallic Triel Elements” Angew. Chem. Int. Ed., 39 (2000), 1246.

U. Häussermann, S. I. Simak, R. Ahuja, B. Johansson, S. Lidin ”The Origin of the Distorted Close-Packed Elemental Structure of Indium” Angew. Chem. Int. Ed., 38 (1999), 2017.

U. Häussermann, S. I. Simak, I. A. Abrikosov, S. Lidin ”The Structure of a -Gallium and its Relation to Deltahedral Clusters” Chem. Eur. J., 3 (1997), 904.

Another research field concerns ICs formed between transition metals and p-block elements. These compounds represent probably the most diverse class of inorganic materials. A wide variety of compositions and structures give rise to a manifold of interesting properties including superconductivity, different forms of magnetism, etc. We have been focusing on compounds with the structure types PtHg 4, Ir 3Sn 7, and FeGa 3. In these materials strong d-p bonding gives rise to a hybridisation gap in the density of states, which is connected to interesting transport properties.

Fig1.: FeGa 3 and CoGa 3 are isostructural (FeGa 3 type). While CoGa 3 is a good metallic conductor, FeGa 3 displays a narrow band gap and is one of the few examples of a semiconducting compound exclusivley composed of geniune metallic elements.

U. Häussermann, M. Boström, P. Viklund, Ö. Rapp, T. Björnängen ”FeGa 3 and RuGa 3 - Semiconducting Intermetallic Compounds” J. Solid State Chem., 165 (2002), 94.

U. Häussermann, P. Viklund, M. Boström, R. Norrestam, S. I. Simak ”Bonding and Properties of Hume-Rothery Compounds with the Simple PtHg 4 Structure” Phys. Rev. B, 63 (2001), 125118.

U. Häussermann, M. Elding-Pontén, C. Svensson, S. Lidin ”Compounds with the Ir 3Ge 7 Structure Type: Interpenetrating Frameworks with Flexible Bonding Properties” Chem. Eur. J., 4 (1998), 1007.