| Project/Area Number |
10640356
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| Research Category |
Grant-in-Aid for Scientific Research (C)
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| Allocation Type | Single-year Grants |
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| Section | 一般 |
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| Research Field |
固体物性Ⅱ(磁性・金属・低温)
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| Research Institution | Fukui University of Technology |
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Principal Investigator |
ENDO Hirohisa Fukui University of Technology, Engineering, Professor, 工学部, 教授 (40025284)
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| Co-Investigator(Kenkyū-buntansha) |
YAMAMOTO Itsuro Hirosaki University, Education, Associate Professor, 教育学部, 助教授 (40210520)
HOSHINO Hideoki Hirosaki University, Education, Professor, 教育学部, 教授 (30001861)
HIWATARI Yasuaki Kanazawa University, Science, Professor, 理学部, 教授 (20019491)
IKAWA Atsushi Kyoto University, Science, Associate Professor, 理学部, 助教授 (80243004)
IKEMOTO Hiroyuki Toyama University, Science, Associate, 理学部, 助手 (20262496)
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| Project Period (FY) |
1998 – 1999
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| Project Status |
Completed (Fiscal Year 1999)
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| Budget Amount *help |
¥2,800,000 (Direct Cost: ¥2,800,000)
Fiscal Year 1999: ¥700,000 (Direct Cost: ¥700,000)
Fiscal Year 1998: ¥2,100,000 (Direct Cost: ¥2,100,000)
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| Keywords | liquid chalcogen / semiconductor to metal transition / phase transition in liquid |
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| Research Abstract |
In recent years, many investigations on liquid chalcogens such as Se and Te have been done. It has been reported that the liquids undergo the semiconductor to meal (S-M) transition at high temperatures, being accompanied by structural transformation. Much of the interest stems from the apparent persistence of two-fold covalent bonding across the S-M transition.
The studies have been focused on the links between the structural aspects of liquid chalcogens and their electronic properties. The extended X-ray absorption fine structure (EXAFS), conductivity and Hall coefficient measurements have been carried out for liquid Te-Se (1-Te-Se) mixtures and liquid As-Te (1-As-Te) mixture. The first-principle molecular-dynamics simulation has been also performed since it provides the microscopic mechanism of the S-M transition.
EXAFS data analysis for 1-Te-Se mixtures reveals that the two-fold chains in the metallic 1-Te-Se shortened by thermal agitation are composed of short and long covalent bonds
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and the long bonds vanish in the semiconducting state. The network structure of the 1-As-Te mixtures with three-fold coordinated Te atoms and two-fold coordinated Te atoms is transformed into the two-fold chain structure. The network-chain transformation is accompanied with the semiconductor to metal transition which is demonstrated by the results for conductivity and Hall coefficient. The radial distribution functions including bond-angle and dihedral-angle distribution for 1-Se are wide temperature and pressure range up to critical point have been determined by the tight-binding molecular dynamic simulation. It has been found that the chain-like structure persists even in metallic state though the average chain length decreased and the dihedral angle has a flatter distribution.
The dangling bonds of Te or the two-fold coordinated as atoms modified by the network-chain transformation cause large fluctuations of the charge distribution in the shortened chains, which results in a frequent inter- and intra-charge transfer. This is our scenario for the source of the S-M transition in the liquid chalcogen mixtures composed of covalently bonded chains. Less
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