関連する実験動画
Updated: May 19, 2026
05:20
Characterization of Thermal Transport in One-dimensional Solid Materials
Published on: January 26, 2014
負の熱膨張 ZrW2O8でオーダーする局所的なWO4の実際の空間分布
Yukio Sato1, Yasuhisa Yamamura, Kazuya Saito
1Institute of Engineering Innovation, The University of Tokyo, 2-11-16 Yayoi, Bunkyo, Tokyo 113-8656, Japan. y_sato@sigma.t.u-tokyo.ac.jp
Journal of the American Chemical Society
|August 18, 2012
まとめ
亜鉛トングステートは,例外的な負の熱膨張 (NTE) を表しています. 新しい電子顕微鏡は,ナノスケールWO(4) 障害がこの現象の鍵であることを明らかにし,そのユニークな性質の洞察を提供しています.
科学分野:
- マテリアルサイエンス 材料科学
- 固体化学 固体化学
- クリスタログラフィーです.
背景:
- 固体は通常加熱時に膨張しますが,例外があります.
- 亜鉛tungstate (ZrW(2) O(8)) は,幅広い温度範囲で著しい負の熱膨張 (NTE) を示す顕著な材料です.
- 以前の研究では,NTEメカニズムにおける金属酸素多面体の役割が強調されたが,顕微鏡の詳細が欠けていた.
研究 の 目的:
- 先進電子顕微鏡を用いて,ZrW(2) O(8) のWO(4) テトラヘッドの局所的な順序を調査する.
- ZrW ((2) O ((8)) での負の熱膨張の顕微鏡的起源を理解するために.
- 現実空間での観測に基づいて,ZrW(2) O(8) の微細構造モデルを開発する.
主な方法:
- 高解像度電子顕微鏡による観測.
- 地元のWO(4) テトラヘッド分布のリアルスペースイメージング.
- ナノスケールの秩序と混乱現象の分析.
主要な成果:
- この研究は,ZrW(2) O(8) での局所的なWO(4) テトラヘッドの順序を初めて直接観察したものである.
- 主要な発見は,部分的に逆転したWO(4) の順序付けと,WO(4) のナノスケールの乱れを含みます.
- スカンジウムドーピングは,WOの程度を高めることが観察されました.
結論:
- 観測されたナノスケールWO(4) 障害は,ZrW(2) O(8) の負の熱膨張の振る舞いを理解するために重要である.
- ZrW(2) O(8) の新しい微細構造モデルが提案され,その局所構造の精巧な視点を提供しています.
- これらの発見は,相変化における局所構造の役割を理解し,熱膨張特性を合わせた材料の設計に不可欠です.
関連する概念動画
01:29Crystallographic Point Groups
Crystallographic point groups represent the various symmetry operations that can occur within crystals. They are unique in that at least one point will always remain unchanged during these actions. For instance, consider the triclinic system. This system, devoid of any axis or plane of symmetry, aligns with the C1 and Ci point groups.where Cᵢ is characterized solely by a center of inversion.Contrastingly, the monoclinic system introduces an element of symmetry. This system with one plane and...
01:29Imperfections in Crystal Structure: Non-Stoichiometric Defects
Non-stoichiometric defects refer to a type of defect in the crystal structure of a compound where the ratio of its constituent elements deviates from the ideal stoichiometric ratio. There are two main types of non-stoichiometric defects: metal excess defects and metal deficiency defects.Metal excess defects occur when there is a slight surplus of metal ions than what is required by the stoichiometric ratio of the compound. For example, heating a sodium chloride crystal in sodium vapor results...
01:26Imperfections in Crystal Structure: Stoichiometric Point Defects
Schottky defects arise when some lattice points in a crystal, such as those in NaCl, remain unoccupied, creating lattice vacancies without disturbing the overall electrical neutrality of the crystal. This defect is common in ionic crystals where the positive and negative ions are similar in size, as seen in sodium chloride and cesium chloride. The presence of Schottky defects enables the crystal to conduct electricity to a small extent through an ionic mechanism. Electric fields cause nearby...
01:27Lattice Energies of Ionic Crystals
Lattice energy represents the energy released when gaseous cations and anions combine to form an ionic solid, reflecting the strength of electrostatic interactions within the crystal. This process is fundamentally governed by Coulombic attraction between oppositely charged ions, where the potential energy varies inversely with the interionic distance and directly with the product of ionic charges. As ions approach one another, the electrostatic energy becomes increasingly negative, indicating a...
02:58Crystal Field Theory - Octahedral Complexes
Crystal Field Theory
To explain the observed behavior of transition metal complexes (such as colors), a model involving electrostatic interactions between the electrons from the ligands and the electrons in the unhybridized d orbitals of the central metal atom has been developed. This electrostatic model is crystal field theory (CFT). It helps to understand, interpret, and predict the colors, magnetic behavior, and some structures of coordination compounds of transition metals.
CFT focuses on...
To explain the observed behavior of transition metal complexes (such as colors), a model involving electrostatic interactions between the electrons from the ligands and the electrons in the unhybridized d orbitals of the central metal atom has been developed. This electrostatic model is crystal field theory (CFT). It helps to understand, interpret, and predict the colors, magnetic behavior, and some structures of coordination compounds of transition metals.
CFT focuses on...
02:46Crystal Field Theory - Tetrahedral and Square Planar Complexes
Tetrahedral Complexes
Crystal field theory (CFT) is applicable to molecules in geometries other than octahedral. In octahedral complexes, the lobes of the dx2−y2 and dz2 orbitals point directly at the ligands. For tetrahedral complexes, the d orbitals remain in place, but with only four ligands located between the axes. None of the orbitals points directly at the tetrahedral ligands. However, the dx2−y2 and dz2 orbitals (along the Cartesian axes) overlap with the ligands less than the dxy,...
Crystal field theory (CFT) is applicable to molecules in geometries other than octahedral. In octahedral complexes, the lobes of the dx2−y2 and dz2 orbitals point directly at the ligands. For tetrahedral complexes, the d orbitals remain in place, but with only four ligands located between the axes. None of the orbitals points directly at the tetrahedral ligands. However, the dx2−y2 and dz2 orbitals (along the Cartesian axes) overlap with the ligands less than the dxy,...