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首页> 外文期刊>Inorganic Chemistry: A Research Journal that Includes Bioinorganic, Catalytic, Organometallic, Solid-State, and Synthetic Chemistry and Reaction Dynamics >Three-Dimensional Modeling of Quasicrystal Structures from X-ray Diffraction: An Icosahedral Al-Cu-Fe Alloy
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Three-Dimensional Modeling of Quasicrystal Structures from X-ray Diffraction: An Icosahedral Al-Cu-Fe Alloy

机译：X射线衍射拟晶体结构的三维建模：ICOSAHEDRAL AL-CU-Fe合金

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摘要

Quasicrystals (QCs) are well-ordered but aperiodic crystals with classically forbidden symmetries (such as 5-fold). High-dimensional (HD) crystallography is a standard method to locate atom positions explicitly. However, in practice, it is still challenging because of its complexity. Here, we report a new simple approach to three-dimensional (3D) atomic modeling derived from X-ray diffraction data, and apply it to the icosahedral QC Al0.63Cu0.25Fe0.12. Electron density maps were calculated directly from 3D diffraction data indexed with noninteger (fractional) numbers as measured, with proper phases; each of 2(5) = 32 possible phase assignments for the five strongest reflections was used for Fourier synthesis. This resulted in an initial phasing model based on chemically sensible electron density maps. The following procedure was exactly the same as that used to determine ordinary crystal structures, except that fractional indices were assigned to the reciprocal vectors relative to the three orthogonal 2-fold axes in icosahedral (I-h) symmetry to which the observed diffraction data conformed. Finally, similar to 30 000 atoms were located within a sphere of a,similar to 48 angstrom radius. Structural motifs or basic repeating units with a hierarchical nature can be found. Isolated icosahedral clusters are surrounded by a concentric dodecahedron, beyond which there is a concentric truncated icosahedron. These are strikingly similar to those obtained via HI) crystallography, but show very clear real-space relationships between the clusters.
机译：拟Crystals（QCS）是有序的，但具有经典禁止的对称性的非周期性晶体（例如5倍）。高维（HD）晶体术是明确定位原子位置的标准方法。然而，在实践中，由于其复杂性，它仍然具有挑战性。在这里，我们报告了从X射线衍射数据导出的三维（3D）原子建模的新简单方法，并将其应用于ICOSAHEDRAL QC AL0.63CU0.25FE0.12。通过测量的阶段直接从用非整数（分数）数量的3D衍射数据计算电子密度图，具有适当的阶段;对于五个最强烈反射的2（5）= 32可能的相位分配用于傅立叶合成。这导致了基于化学合理的电子密度图的初始分阶段模型。以下步骤与用于确定普通晶体结构的方法完全相同，不同之处在于将分数指数相对于互核载体（I-H）对称性的三个正交2折轴分配给互易型载体，以至于观察到的衍射数据符合的衍射数据。最后，类似于30 000原子位于类似于48埃半径的球体内。可以找到具有分层性质的结构主题或基本重复单元。孤立的icosaheDral群集被同心十二锭围住，超出了一个同心截断的icosahedron。这些与通过Hi）晶体学相似的非常相似，但在簇之间显示出非常明显的实际关系。

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