Development of Diffraction Techniquesfor Studying Phase Transformation (Synchrotron Radiation and High-Resolution Electron Microscopy)

1)将欧米伽型磁体引入常规电子显微镜，建立了能量过滤电子衍射法。用这种方法可以消除非弹性散射引起的电子衍射中的强本底，并且可以定量地分析由相变引起的复杂的漫射散射。例如，用能量过滤电子衍射和原位暗场电子显微镜研究了前驱体对Ti50Ni48Fe2马氏体相变的影响，首次阐明了含有横向原子位移的微区的存在和生长过程。用能量过滤电子衍射法定量测定了Cu3Pd的短程有序参数。2)形核和生长过程动力学是研究非平衡态一级相变机制的有效途径。在Au-47.5at%Cd-0.75at.Cu单晶上，用高灵敏度的探测器和精确的温控器获得了原位X射线衍射数据。3)高角环形探测器暗场扫描电子显微镜作为高分辨电子显微镜的一种新技术，被广泛应用于十方准晶的结构研究。我们发现了有序准晶，这可以从氯化钠和氯化铯类型的超立方晶格的投影中得到解释。

The results in the present work are summarized as follows.1) By introducing the omega-type magnet into a conventional electron microscope, the energy-filtering electron diffraction method was established. With this method, the strong background in the electron diffraction due to the inelastic scattering could be removed and complicated diffuse scattering resulting from the phase transformation could now be analyzed quantitatively. For example, the precursor effects on the martensitic transformation in Ti50Ni48Fe2 were investigated by the energy-filtering electron diffraction and in situ dark field electron microscopy, and the existence and the growth process of microdomains containing a transverse atomic displacement were clarified for the first time. Also, the short-range order parameter in Cu3Pd was determined quantitatively by the energy-filtered electron diffraction method.2) The kinetics on the nucleation and growth process is an effective approach to investigate the mechanism of first-order phase transformations for non-equilibrium state. In-situ X-ray diffraction data with an accurate temperature controller and highly sensitive detector attached to rota-unit has been obtained from Au-47.5 at%Cd-0.75at.Cu single crystal. It is understood that the nucleus of the low-temperature phase starts from the surface and grows into the inner part gradually.3) High-angle annular detector dark-field scanning transmission electron microscopy, which is much attention as a new technique for high-resolution electron microscopy, is applied for studying the structure of decagonal quasicrystals. Ordered quasicrystals, which can be interpreted from the projection of NaCl-and CsCl-type hypercubic lattices, have been found.