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전이금속 칼코겐 화합물의 합성과 구조해석 및 특징
- Author(s)
- 김경희
- Advisor
- 윤호섭
- Department
- 일반대학원 에너지시스템학부
- Publisher
- The Graduate School, Ajou University
- Publication Year
- 2011-02
- Language
- eng
- Alternative Abstract
- New transition metal thiophosphates have been prepared with the use of eutectic alkali metal halide fluxes (KCl/LiCl or RbCl/LiCl or CsCl/LiCl) and their crystal structures have been structurally investigated by single crystal X-ray diffraction techniques. Ax(Ta1-yTiy)PS5 (A = K, Rb) are isostructural with the previously reported A0.42TaPS5 (A = K, Rb) but the Cs analogue, Csx(Ta1-yTiy)PS5 shows lower symmetry due to the large size and strong electropositivity of Cs atoms. Ax(Ta1-yTiy)PS5 (A =K, Rb) crystallize in the orthorhombic space group Fddd with sixteen formula units whereas Ax(Ta1-yTiy)PS5 (A =Cs) crystallizes in the monoclinic space group P21/n with eight formula units. The structure of AxTa1-yTiyPS5 is built up from the dimeric [M2S10] units (M=Ta or Ti) composed of edge-sharing [MS6] octahedra. These units are linked by sharing common edges with four tetrahedral [PS4] groups yielding a two-dimensional layer. These layers are stacked on top of each other to create van der Waals gaps and the alkali metal ions reside in this space. Electrons are transferred from the alkali metals to the mixed Ta/Ti sites and the stoichiometry of the phases can be controlled systematically with the use of the difference of electropositivities and sizes of each alkali metal. Eventually the amount of alkali metal restricts the composition of the metals. The title compounds exhibit absorption band gaps of 1.6eV~1.7eV and these phases can be classified as semiconductors. The new one-dimensional compounds, RbCrPS5 and CsCrPS5, crystallize in the space group of the monoclinic with four formula units. The structures consist of one-dimensional chains separated by alkali metal cations. The linear chains are built up from the basic repeating unit, [Cr2(PS4)2S2]2-, which is composed of a pair of edge-sharing Cr-centered octahedra and a P-centered tetrahedron. Basic units of ACrPS5 (A = Rb, Cs), [Cr2(PS4)2S2]2- are similar to those of the ATiPS5 (A = K, Rb). These repeating units are linked together sharing two μ2-S atoms to form the one-dimensional chain. They are stabilized through ionic interactions with cations. Thus there is no inter-chain bonding interactions except the van der waals forces. The classical charge balance of the title compound can be described as [A+][Cr4+][P5+][S2-]5, (A = Rb, Cs). UV/Vis diffuse reflectance measurements indicate that they are semiconductors with optical band gaps of ca. 1.4 eV, whchi is compatible with the dark brownish color of the crystals. The paramagnetic behavior of the compound has been established from variable-temperature magnetic susceptibility data in the temperature range of 5-300 K. The origin of the magnetic property should be the two t2g electrons of the Cr4+ ion. The new thiophosphate, CsCrP2S7 crystallizes in the space group -C2 of the monoclinic system in a cell of a=8.5801(5) Å, b=9.5345(6) Å, c=6.7449(6), β=97.530(3), V=547.02(7) Å3. This compound comprises two-dimensional layers separated from one other by Cs+ cations. The layers are built up from the basic repeating unit , which is composed of bitetrahedral [P2S7] units sharing edges and corners with [CrS6] octahedra. The alkali metal cations (Cs+) are coordinated by eight sulfur atoms, four from each the two [CrP2S7] adjacent layers. The classical charge balance of the compound can be described as [Cs+][Cr3+][P5+]2[S2-]7.
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- Graduate School of Ajou University > Department of Energy Systems > 3. Theses(Master)
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