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Abstract
The atomic structure, energetics and chemical bonding state of pristine and Y doped Σ13, (104) grain boundaries in α-Al2O3 were investigated by aberration-corrected Z-contrast scanning transmission electron microscopy combined with first-principles calculations. Combining observations from two orthogonal directions parallel to the grain boundary plane, we found that Y atoms segregate into specific atomic sites and form two-dimensionally ordered structure. We performed first-principles calculations to estimate stable atomic sites for Y segregation, and it was found that the calculation results are in good agreement with the experimental results. Local chemical bonding states at the core of the boundary were investigated by a first-principles orthogonalized linear combination of atomic orbitals (OLCAO) method, and Y atoms and neighboring O atoms were found to evince strong ionic character while O–Al back bonds evince strong covalent character.
Acknowledgements
This work was supported by the Grant-in-Aid for Scientific Research from the Ministry of Education, Culture, Sports and Technology (MEXT) and Japan Society for the Promotion of Science (JSPS). We would like to thank Prof. W. Y. Ching at the University of Missouri-Kansas City for use the OLCAO code. Some calculations were performed by the Super Computer Center of the Institute of Solid State Physics (ISSP), The University of Tokyo. This work was conducted in the research Hub for Advanced Nano Characterization, The University of Tokyo, supported by MEXT. S.D.F. acknowledges support by the Australian Research Council.