Li Mingrun, Sun Junliang, Oleynikov Peter, Hovmöller Sven, Zou Xiaodong, Grushko Benjamin
Structural Chemistry, Stockholm University, SE-106 91 Stockholm, Sweden.
Acta Crystallogr B. 2010 Feb;66(Pt 1):17-26. doi: 10.1107/S0108768109053804. Epub 2010 Jan 22.
The structure of a complicated quasicrystal approximant epsilon(16) was predicted from a known and related quasicrystal approximant epsilon(6) by the strong-reflections approach. Electron-diffraction studies show that in reciprocal space, the positions of the strongest reflections and their intensity distributions are similar for both approximants. By applying the strong-reflections approach, the structure factors of epsilon(16) were deduced from those of the known epsilon(6) structure. Owing to the different space groups of the two structures, a shift of the phase origin had to be applied in order to obtain the phases of epsilon(16). An electron-density map of epsilon(16) was calculated by inverse Fourier transformation of the structure factors of the 256 strongest reflections. Similar to that of epsilon(6), the predicted structure of epsilon(16) contains eight layers in each unit cell, stacked along the b axis. Along the b axis, epsilon(16) is built by banana-shaped tiles and pentagonal tiles; this structure is confirmed by high-resolution transmission electron microscopy (HRTEM). The simulated precession electron-diffraction (PED) patterns from the structure model are in good agreement with the experimental ones. Epsilon(16) with 153 unique atoms in the unit cell is the most complicated approximant structure ever solved or predicted.
通过强反射方法，从已知的相关准晶近似物ε(6)预测了复杂准晶近似物ε(16)的结构。电子衍射研究表明，在倒易空间中，两种近似物的最强反射位置及其强度分布相似。通过应用强反射方法，从已知的ε(6)结构的结构因子推导出ε(16)的结构因子。由于两种结构的空间群不同，为了获得ε(16)的相位，必须应用相位原点的偏移。通过对256个最强反射的结构因子进行傅里叶逆变换，计算出了ε(16)的电子密度图。与ε(6)类似，预测的ε(16)结构在每个晶胞中包含八层，沿b轴堆叠。沿b轴，ε(16)由香蕉形瓦片和五边形瓦片构成；这种结构通过高分辨率透射电子显微镜（HRTEM）得到了证实。从结构模型模拟的进动电子衍射（PED）图案与实验图案吻合良好。晶胞中含有153个独特原子的ε(16)是迄今解析或预测出的最复杂的近似物结构。
