| Budget Amount *help |
¥1,900,000 (Direct Cost: ¥1,900,000)
Fiscal Year 1992: ¥400,000 (Direct Cost: ¥400,000)
Fiscal Year 1991: ¥1,500,000 (Direct Cost: ¥1,500,000)
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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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