Atomic structure, energetics, and chemical bonding of y doped Σ13 grain boundaries in α-Al₂O₃

The atomic structure, energetics and chemical bonding state of pristine and Y doped Σ13, (10 4) grain boundaries in α-Al₂O ₃ 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.