X-ray structural analysis of three dimensional quasicrystals

在三维准晶体中，所谓的Mackay型和TC型准晶体的原子结构正趋于理解为具有二十面体对称的原子团簇的准周期排列，这在本小组提出的QCIC（准周期配置的二十面体簇）模型中是典型的。所谓的f型准晶体是最近发现的三维准晶体，其结构仍然是未知的。本研究的目的是分析Al-Cu-Fe、Al-Cu-Ru和Al-Pd-Mn合金体系中f型准晶的原子结构，并与传统的Mackey型准晶结构进行比较，建立其结构模型。x射线衍射实验在KEK的光子工厂进行。用粉末样品测量了衍射剖面。在Al-Cu-Ru和Al-Pd-Mn体系中，分别测量了Ru边缘和P…More d边缘的x射线异常散射，以获得Ru和Pd原子周围的环境结构。用Bridgeman法成功地生长了Al-Pd-Mn体系的单晶，并测量了单晶的衍射。x -射线衍射谱显示出来自准晶体有序结构的奇指数额外峰。根据轮廓计算了总对分布函数和环境对分布函数。详细分析表明，f型准晶体的局部结构与传统的Mackay型准晶体非常相似，这表明f型准晶体也是由二十面体簇的准周期结构组成的。建立了Al-Cu-Ru和Al-Pd-Mn体系的f型准晶体模型，其中两种二十面体团簇准周期性排列，并根据指数宇称分布在两种准晶格点上。模型较好地再现了实验得到的衍射曲线、对分布函数和其他参数值，表明模型的框架反映了f型准晶体的真实结构。少

Among the three dimensional quasicrystals, so called Mackay type and TC type quasicrystals are settling to the understanding of their atomic structures to be quasiperiodic arrangements of the atomic clusters with icosahedral symmetry, which are typically seen in QCIC (Quasiperiodic Configuration of Icosahedral Clusters) model proposed by the present group. The structures of so called F-type quasicrystals, which are recently discovered three dimensional quasicrystals, are still remained unknown.The objective of the present study is to analyze the atomic structures of the F-type quasicrystals in Al-Cu-Fe, Al-Cu-Ru and Al-Pd-Mn alloy systems in comparison with the structure of conventional Mackey type quasicrystals and to construct the structural models.The X-ray diffraction experiments were performed in Photon Factory of KEK. The diffraction profile was measured with powder samples. In the case of Al-Cu-Ru and Al-Pd-Mn systems, X-ray abnormal scattering was also measured at Ru edge and P … More d edge, respectively, in order to obtain the environmental structures around Ru and Pd atoms. Single crystals of the Al-Pd-Mn system were successfully grown by Bridgeman method and the diffraction was measured also for the single crystal.The X-ray diffraction profiles present the extra peaks with odd indices that come from the ordered structures in the quasicrystals. The total pair distribution functions and the environmental pair distribution functions were calculated from the profiles. The detailed analysis revealed that the F-type quasicrystals have very similar local structures to those in the conventional Mackay type quasicrystals, which indicates that the F-type quasicrystals are also consist of quasiperiodic configurations of icosahedral clusters.The models for F-type quasicrystals of Al-Cu-Ru and Al-Pd-Mn system were made, in which the two kinds of icosahedral clusters are arranged quasiperiodically and the clusters are distributed to the two kinds of quasilattice points according to the parity of the indices.The models reproduced well the diffraction profiles, pair distribution functions and the values of other parameters experimentally obtained, which indicates the framework of the models reflects the real structures of the F-type quasicrystals. Less