Study of Microscopic Pattern Formation in Structural Phase Transition by Electron Microscopy

本研究的目的是研究在几种结构相变中出现的微观图案的结构和物理性质，并利用带有纳米尺寸探针的电子显微镜来发现其图案形成的动力学特性。主要结果分为以下三类。用电视摄像系统和成像板系统观察了Rb_2ZnCl4和BaZnGeO_4在C-IC相变过程中非公度(DC)晶格的花样演化，并从暗场图像和衍射图中的漫射光强分布的分析研究了它们的性质。观察到了条纹和反条纹的产生和湮灭，以及伴随DC重排而产生的条纹和平面DC之间的相互作用。几个相变中的新发现--发现电子束…在BaZn GeO4中，随着辐照次数的增加，出现了至少三种不同的相结构。在Pb3(PO4)2中，在铁弹性相变温度以上用扩散散射获得了高分辨率的图像，这表明铁弹性相微区的存在。在Ba2NaNb5015的C-IC相变中，发现在IC相中产生了尺寸为10 nm的铁弹磁畴，这导致了IC相的四方对称性和qusi2-q态。通过观察直流电和铁弹磁畴壁的运动，研究了IC-C的相变和记忆效应。微观区域的物理测量我们试图发展一种测量纳米尺度区域的物理性质的方法，以及通过电子显微镜观察得到的结构性质。研究发现，利用精细会聚电子束的集光系统探测到的切伦科夫辐射和跃迁辐射将提供纳米尺度区域介电函数的信息。较少

The purpose of this research is to study structural and physical properties of microscopic patterns arising in several structural phase transitions, and to find the dynamical properties of their pattern formations by means of an electron microscope with a nanometer-size probe. The main results are divided into the following three categories.1. Pattern formation in commensurate-incommensurate phase transitionPattern evolution of the discommensuration(DC) lattices during the C-IC phase transitions in Rb2ZnCl4 and BaZnGeO4 was observed and their properties were studied from the analyzes of the dark field images and also the diffuse intensity profiles in the diffraction patterns, using the TV camera system and the imaging plate system. The creation and annihilation of stripples and antistripples were seen and the interactions between stripple and planer DC were observed, which accompany the rearrangements of DCs.2. New founding in several phase transitionsIt is found that the electron beam … More irradiation induces phase transition in BaZn GeO4, and at least three distinct phases were observed to appear. In Pb3(PO4)2 the high resolution image using the diffuse scattering was taken above the ferroelstic phase transition temperature, which indicates the existence of microdomains of the ferroelastic phase. In the C-IC phase transition of Ba2NaNb5015 the ferroelastic domains of the order of 10nm in size are found to be created in the IC phase, which result in the tetragonal symmetry and the qusi2-q state of the IC phase. The IC-C phase transition and the memory effect were studied through the observation of DC and ferroelastic domain wall motion.3. Physical measurement of microscopic regionWe try to develop the method to measure physical properties of nanoscale region as well as the structural properties obtained from the electron microscopic observation. It is found that the Cherenkov and transition radiation detected by the light collection system using a finely converged electron beam will provide information of the dielectric function of a nanoscale region. Less