| 研究実績の概要 |
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.
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