Kaoru Kimura Professor
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|applied solid state physics, nano-space function design, structurally complex material, thermoelectric materials, icosahedral cluster, quasicrystal|
We found that icosahedral clusters of boron and aluminum have metallic or covalent bonds depending on the existence of a central atom in the cluster, and proposed a concept "metallic-covalent bonding conversion". On the other hand, the symmetry of the icosahedral cluster cannot coexist with the periodicity of the crystal. In boron- and aluminum-based compounds composed of icosahedral clusters, there are several phases continuously from metal to semiconductor and from crystal to quasicrystal. These compounds are rich in variety and are expected to yield new functional materials. We joined these two groups of materials to be one group of icosahedral cluster solids, and are trying to construct a unified picture by analyzing the structures, investigating the electronic states using first-principle molecular orbital and band-structure calculations, obtaining the electron density distribution using the MEM/Reitvelt method and measuring the electrical, optical and thermal properties. We are developing new functional materials taking advantage of the characteristics of icosahedral cluster solids, i.e., a thermoelectric material and a highly resistive chip material using the intermediate properties between a metal and a semiconductor, and a superconducting material using the high symmetry of the icosahedron.
K. Kitahara and K. Kimura: "Local cluster networks and the number of valence states in aluminium-transition metal face-centred icosahedral quasicrystals", Zeitschrift fuer Kristallographie 232, 507-513 (2017). (Invited paper)
K. Kitahara, Y. Takagiwa, and K. Kimura: "Semimetallic Band Structure and Cluster-Based Description of a Cubic Quasicrystalline Approximant in the Al-Cu-Ir System", Journal of the Physical Society of Japan 84, 014703-1-8 (2015).
Y. Takagiwa and K. Kimura: "Metallic-covalent bonding conversion and thermoelectric properties of Al-based icosahedral quasicrystals and approximants", Science and Technology of Advanced Materials 15, 044802-1-12 (2014). (Review paper)