2015-Sustainable Industrial Processing Summit
SIPS 2015 Volume 8: Composite & Ceramic, Quasi-crystals and Nanomaterials
| Editors: | Kongoli F, Pech-Canul M, Kalemtas A, Werheit H |
| Publisher: | Flogen Star OUTREACH |
| Publication Year: | 2015 |
| Pages: | 300 pages |
| ISBN: | 978-1-987820-31-7 |
| ISSN: | 2291-1227 (Metals and Materials Processing in a Clean Environment Series) |
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Metallic-Covalent Bonding Conversion and Thermoelectric Properties of Al-Based Icosahedral Quasicrystals and Approximants
Kaoru Kimura1;1THE UNIVERSITY OF TOKYO, Chiba, Japan;
Type of Paper: Regular
Id Paper: 205
Topic: 8
Abstract:
In this talk, we review the characteristic features of icosahedral cluster solids, metallic-covalent bonding conversion (MCBC) and the thermoelectric properties of Al-based icosahedral quasicrystals and approximants. MCBC is clearly distinguishable from and closely related to the well-known metal-insulator transition. This unique bonding conversion has been experimentally verified in 1/1-AlReSi and 1/0-Al12Re approximants by the maximum entropy method and Rietveld refinement for powder x-ray diffraction data and is caused by a central atom inside the icosahedral clusters. This helps to understand pseudogap formation in the vicinity of the Fermi energy and establish a guiding principle for tuning the thermoelectric properties. From the electron density distribution analysis, rigid heavy clusters weakly bonded with glue atoms are observed in the 1/1-AlReSi approximant crystal, whose physical properties are close to icosahedral Al-Pd-TM (TM: Re, Mn) quasicrystals. They are considered to be an intermediate state among the three typical solids: metals, covalently bonded networks (semiconductor) and molecular solids. Using the above picture and detailed effective mass analysis, we propose a guiding principle of weakly bonded rigid heavy clusters to increase the thermoelectric figure of merit (ZT) by optimizing the bond strengths of intra- and intericosahedral clusters. Through element substitutions that mainly weaken the inter-cluster bonds, a dramatic increase of ZT from less than 0.01 to 0.26 was achieved. To further increase ZT, materials should form a real gap to obtain a higher Seebeck coefficient.