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새로운 2 차원 사성분계 황화물의 합성 및 구조 연구
- Alternative Title
- Bae Sanghyun
- Author(s)
- 배상현
- Alternative Author(s)
- Bae Sanghyun
- Advisor
- 윤호섭
- Department
- 일반대학원 에너지시스템학과
- Publisher
- The Graduate School, Ajou University
- Publication Year
- 2020-02
- Language
- eng
- Alternative Abstract
- Chalcogens (S, Se, and Te) are less electronegative and more polarizable compared with oxygen and they show greater covalencies and inter-chalcogen interactions. As a result, chalcogenides prefer low-dimensional structures and usually they have anisotropic structures and properties. Research in the alkali metal transition metal chalcogenides have been a very active area for two decades due to their unusual structural features and the novel physical properties. However, no quaternary alkali metals/early transition metals/ palladium chalcogenide has ever been reported yet. In our laboratory, we have prepared a number of multinary chalcogenides with the use of alkali metal halide as reactive fluxes and we were able to prepare new phases in this family. The new quaternary palladium sulfides, K2Ta6Pd9S24 and Cs2HfPd3S6 have been prepared from elemental powders through alkali metal halide flux methods and they are structurally characterized by single crystal X-ray diffraction techniques. They adopt two-dimensional layered structures. In these layers, the early transition metals of the groups 4 or 5 (Hf, Ta) are surrounded by six S atoms in a trigonal prismatic fashion and the Pd atoms are coordinated to four square planar S atoms. The structural diversity of these compounds come from the different connecting mode of these building blocks. In chapter I, synthesis and structure of the quaternary palladium sulfides, Cs2HfPd3S6 is discussed along with the related phases, Cs2ZrPd3S6 and CsTaPd3S6. For Cs2HfPd3S6, two HfS6 units are bridged by two Pd atoms by sharing edges to form the basic repeating units, Hf2Pd2S12. These units are linked together to complete the infinite anionic two-dimensional layer, 2¦∞[HfPd3S62-]. These layers stack on top of each other and the Cs+ ions reside between the layers to satisfy the charge neutrality to complete the structure. Replacement of tetravalent Hf4+ or Zr4+ with pentavalent Ta5+ has led to a new phase, CsTaPd3S6. In this compound, the layer, 2¦∞[TaPd3S6-] remains intact but the content of alkali metals should be reduced half to satisfy the charge neutrality. There is no strong S-S bonding interaction in these phases and assigning oxidation states of each element is clear. The charge valence of the compounds can be described as [Cs+]2[M4+][Pd2+]3[S2-]6 (Hf, Zr) and [Cs+][Ta5+][Pd2+]3[S2-]6. In chapter II, for K2Ta6Pd9S24, two trigonal prismatic TaS6 units are bridged by two Pd atoms by sharing edges to form the basic repeating units, Ta2Pd2S12. They are connected via Pd atoms to form a two-dimensional layer, 2¦∞[Ta6Pd9S242-]. These layers are separated by K+ ions through electrostatic coulombic interactions. Assigning the oxidation state of Ta in this compound is not straightforward. Especially, the oxidation state of Ta cannot be fixed as an integer. Consequently, we propose a randomly disordered mixed-valence model composed of 2/3 Ta5+ and 1/3 Ta4+ ions and the charge valence of the compound can be described as [K+]2[Ta4+]2[Ta5+]4[Pd2+]9[S2-]24.
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- Graduate School of Ajou University > Department of Energy Systems > 3. Theses(Master)
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