透過型電子顕微鏡による、セラミックス粒界構造解析

在本研究中，我们制备了一种双晶，上下晶体之间的双晶关系为（310）[001]||(310)[001]。衍射图分析证实了这些取向在一个小的失配倾斜角内，高分辨率透射电镜（HRTEM）显示了原子水平上的完美连接。MgO双晶晶界（GB）的HRTEM图像表明，MgO原子在GB上对称排列，并且在GB上以0.62 nm的间隔周期性排列较强的亮点。由于这种原子的周期性排列是Σ5 GB的特性，我们可以确认制造了Σ5对称倾斜GB。此外，从HAADF （high - angle - annulal -暗场）和EELS （Electron energy loss Spectroscopy）成像中可以发现，极少量的钙（Ca）和钛（Ti）原子杂质在GB下同时分离，并在原子尺度上形成了自然三维结构中不存在的有序阵列。根据理论计算，缺陷与电荷强结合，形成复杂稳定的结构。这种结构导致烧结材料性能的显著变化。具有这种稳定结构的强结合晶界将提高块状材料的强度。发现陶瓷晶界中微量的杂质会使有序的上层结构自组装，极大地影响陶瓷材料的物理性能。

In this study, we fabricated a bicrystal, possessing bi-crystallographic relations of (310)[001]||(310)[001] between upper and lower crystals. Analysis of diffraction patterns confirms these orientations to within a small misfit tilt angle, and high-resolution TEM(HRTEM) reveals a perfect joining at atomic level. The HRTEM image of the grain boundary(GB) of the MgO bicrystal shows that MgO atoms were arranged symmetrically on the GB and the stronger bright spots are arranged periodically at intervals of 0.62 nm on the GB. Since this periodic arrangement of atoms is the very property of the Σ5 GB, we can　confirm that a Σ5 symmetric tilt GB is manufactured. In addition, from the HAADF (High-Angle-Annular-Dark-Field) and EELS (Electron Energy-Loss Spectroscopy) mapping images, the very small amount impurities of calcium (Ca) and titanium (Ti) atoms are segregated at the GB at the same time, and formed the ordered array at the atomic scale which was not present in the natural three-dimensional structure. According to the theoretical calculations, the defects and the charge were strongly combined and formed a complex stable structure. This structure results in a significant change in properties of the sintered material. The strongly bound grain boundary which has such a stable structure, will increase the strength of the bulk material. It was found that the trace amounts of impurities in the ceramic grain boundary will make the ordered superstructure self-assembled, and greatly affect the physical properties of the ceramics materials.