Structural Analysis on Quasicrystals and their Approximants.

自Schetman首次在Al-Mn体系中发现准晶体以来，为了了解这种新材料的物理化学性质，人们进行了大量的结构研究。传统的高分辨率电子显微镜被认为是分析准晶体及其近似物结构最有效的方法之一。然而，详细的结构信息，如过渡金属的分布不能从电子显微镜的结果中获得。另一方面，x射线衍射使我们能够确定单个成分的精确原子坐标，这些信息对于讨论准晶体的各种物理性质是非常必要的。在这种背景下，本研究项目的主要目的是利用高分辨率电子显微镜和x射线衍射相结合的方法来表征准晶体及其近似物的结构。此外，本文还大量使用了包含高维空间群论的更多方法来解释所得到的结构结果。为了测量x射线衍射的强度，我们研制了一种新型的配有成像板和成像板强度读取器的weissenberg照相机。采用最大负载18kW的旋转阳极式x射线发生器作为x射线源，在入射光束通道设置石墨单色仪，选择MoKalpha辐射。安装了两个成像板，与传统的四圆衍射仪相比，测量时间大大减少。此外，还介绍了无特殊盲区的多轴控制系统。利用weissenberg相机，我们在Al-Pd-Mn体系中发现了直径分别为1.2nm和2.0nm的十二面体原子团簇。通过表明原子簇大小的tau膨胀规律，将这些原子簇划分为相应二十面体相的基本结构单元。利用这些原子团簇结合投影法建立的结构模型，证明了Al-Pd-Mn二十面体准晶体的结构模型是可行的。这些结果得到了许多材料科学家的赞赏，我们被邀请在1997年准晶体国际会议上讨论这些成果。这些具有十二面体对称性的原子团簇结合投影法，有助于对二十面体准晶体的真正认识。少

Since the first finding of a quasicrystal in Al-Mn system by Schetman, a number of structural studies have been carried out in order to understand the physico-chemical properties of this new materials. The conventional high-resolution electron microscope is known to be one of the most powerful methods to analyze the structures of quasicrystals and their approximants. However, detailed structural information such as transition metal distribution cannot be obtained from the results of the electron microscope only. On the other hand, X-ray diffraction allows us to determine the precise atomic coordinates for individual constituents and such information is strongly required for discussing a variety of physical properties of quasicrystals. In these contexts, the main purpose of this research project is to characterize the structures of quasicrystals and their approximants by the combination of high-resolution electron microscope and X-ray diffraction. It may be added that the projection met … More hod including high dimensional space group theory is intensively used for elucidate the obtained structural results. For the intensity measurement of X-ray diffraction, we developed a new type of weissenberg camera equipped with imaging plates and the intensity reader for them. The rotating anode type X-ray generator with a maximum load of 18kW is employed as a X-ray source, the graphite monochromator is set in the incident beam pass for selecting MoKalpha radiation. Two imaging plates are installed and the measuring time is extensively reduced in comparison with a conventional four-circle diffractometer. It should be added that the mu-axis controlling system is also introduced for the intensity measurement with no special blind region. By using this weissenberg camera, we foundan dodecahedral atom clusters with 1.2nm and 2.0nm in diameter in Al-Pd-Mn system. These atom cluster are classified as essential structural units for the corresponding icosahedral phase, by indicating tau-inflation rule in their sizes. The structural model by using these atom clusters coupled with the projection method allows us to demonstrate a feasible structural model of Al-Pd-Mn icosahedral quasicrystals. These results were appreciated by many material scientists and we are invited to talk these fruitful results at the international conference of quasicrystals in 1997. These atom clusters with dodecahedral symmetry together with a projection method are suggested to shed light upon the real understanding of icosahedral quasicrystals. Less