1988 Fiscal Year Final Research Report Summary
Syntheses and Mechanism of Electric Conduction of 2-Dimensional Mixed Metal Chalcogenides
| Project/Area Number |
62470060
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| Research Category |
Grant-in-Aid for General Scientific Research (B)
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| Allocation Type | Single-year Grants |
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| Research Field |
無機工業化学
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| Research Institution | Tokyo Institute of Technology |
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Principal Investigator |
ATAKE Tooru The Research Laboratory of Engineering Materials, Tokyo Institute of Technology ・ Associate Professor, 工業材料研究所, 助教授 (30028229)
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| Co-Investigator(Kenkyū-buntansha) |
ITO Yoshitaka The Research Laboratory of Engineering Materials, Tokyo Institute of Technology, 工業材料研究所, 助手 (70016822)
MARUYAMA Toshio Faculty of Engineering, Tokyo Institute of Technology ・ Associate Professor, 工学部, 助教授 (20114895)
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| Project Period (FY) |
1987 – 1988
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| Keywords | AgCrS_2 / CucrS_2 / Ag_XCu_<1-X>CrS_2 / NaCrS_2 / Order-disorder phase transition / 相強磁性相転移 |
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| Research Abstract |
In a family of layered chalcogenide compounds of type MCrX_2(M=Ag, Cu, Li, Na, K; X=S, Se), CrX_2 forms sandwich-layers of trigonal symmetry, between which the monovalent cations are intercalated. The cations Ag, Cu are located on the tetrahedrally coordinated sites which form puckered honeycomb lattices. In the case of M=Li, Na and K, the cations are located on the octahedrally coordinated sites which from trigonal lattices. The purpose of this research is to clarify the relationship between of the structure and the ion conduction mechanism, and the other properties of the compounds.
High-purity samples of AgCrS_2 and CuCrS_2 were synthesized directly from the elements in a fused-silica tube at 1270 K. The measurements were carried out for high temperature electric conductivity and heat capacity by adiabatic calorimetry from 7 to 327 K and by ac calorimetry from room temperature up to 720 K. An order-disorder phase transition has been observed at 673 K in AgCrS_2 and 691 K in CuCrS_2.
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The heat capacity anomaly is of a typical second-order transition associated with little fluctuation in the order parameters at the transition points. The mechanism of the transition has been discussed in terms of the critical exponents. The value of the defect formation enthalpy in AgCrS_2 were determined from the excess heat capacities below the transition temperature. The antiferromagnetic-paramagnetic phase transition has been detected as a diffused first-order type of anomaly at 42.02 K in AgCrS_2 and 37.42 K in CuCrS_2. The value of transition entropy indicates that the ordering of the magnetic spins is well established through the phase transition. The phase diagram of Ag_xCu_<1-x>CrS_2 system has been studied by DTA and powder X-ray diffraction. High-purity samples of NaCrS_2 were also synthesized with Na_2-S flux and characterized by using X-ray diffraction and DTA. Heat capacity measurements were made between 7 to 300 K, and the results have been analyzed and discussed in detail. Less
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