1992 Fiscal Year Final Research Report Summary
Neutron and X-ray Diffractions of The Liquid Tl-S System
| Project/Area Number |
03650537
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| Research Category |
Grant-in-Aid for General Scientific Research (C)
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| Allocation Type | Single-year Grants |
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| Research Field |
金属精錬・金属化学
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| Research Institution | Yamagata University |
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Principal Investigator |
UEMURA Osamu Yamagata University, Faculty of Science, Professor, 理学部, 教授 (30007166)
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| Project Period (FY) |
1991 – 1992
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| Keywords | Metal-nonmetal transition / Liquid semiconductor / Amorphous semiconductor / Neutron diffraction / X-ray diffraction |
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| Research Abstract |
Both neutron and X-ray diffraction measurements of liquid Tl_2S, Tl_4S_3, TlS and TlS_2 have been made to investigate the short-range order in the metal-nonmetal transition liquid system, Tl-S. In liquid Tl_2S the local atomic configuration in the crystalline phase substantially remains unchanged on melting, which leads to the metal-nonmetal transition at this composition. The short-range order in liquid Tl_4S_3 and TlS exhibits a considerably different structure from that in their crystalline phases characterized by the tetrahedral TlS_4 molecular units. The structure of these tree liquids is roughly similar, that is to say, the Tl-S bond containing in these liquids has a common nature. This is considered to relate strongly to the composition- independent electrical conductivity observed in this composition range of this liquid system. Liquid TlS_2 also has no TlS_4 molecular units formed in its crystalline phase. Instead, this liquid has a strong covalent S-S bond identical to that in liquid sulfer. Therefore , liquid TlS_2 is expected to be a poor electronic conductor, different from other three liquids, due to the presence of the S-S bond.
The amorphous structure at the compositions of TlS, Tl_2S_3, TlS_2, Tl_3S_7 and Tl_2S_5 has been investigated by the X-ray diffraction measurement. The results obtained are summarized as follows: (1)Amorphous TlS_2 consists of TlS_4 tetrahedral units, similar to the case in its crystal. (2)The existence of these TlS_4 units is confirmed at all compositions investigated. (3)The covalent S-S bond appeared in liquid TlS_2cannot be found in the amorphous state with the same composition. However, this bond is observed in the amorphous alloys with extremely high S content more than Tl_3S_7.
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