X-ray absorption fine-structure study on the fine structure of lutetium segregated at grain boundaries in fine-grained polycrystalline alumina

Abstract

Local atomic structures around the Lu³⁺ ion in a 0.1 mol% LuO_1.5-doped fine-grained Al₂O₃, in which the doped Lu³⁺ ions segregate to the grain boundaries, was characterized by Lu L₃-edge X-ray absorption fine structure. Structural parameters in LuO_1.5-doped Al₂O₃ were determined by a curve-fitting method, and the results showed that six O²⁻ ions coordinate with the Lu ion in LuO_1.5-doped Al₂O₃. In addition, it was also revealed that the Lu–O interatomic distance in Lu-doped Al₂O₃ was close to that in Lu₂O₃, which was about 19% longer than the Al–O interatomic distance in undoped Al₂O₃. The present results indicated that the local atomic structures around Lu in Al₂O₃ are close to that in Lu₂O₃. It is thus supposed that atomic distances between Al³⁺ and O²⁻ ions in the vicinity of Lu-segregated grain boundaries are shortened in comparison with that in undoped Al₂O₃. A first-principles molecular orbital calculation was performed for the [Al₂O₉]⁻¹² model cluster, and the shortening of the Al–O interatomic distance was found to have an effect of increasing the ionicity in Al³⁺ ions.

Acknowledgements

The authors wish to express their gratitude to the Ministry of Education, Culture, Sports, Science and Technology and Japan Society for the Promotion of Science for the financial support by a grant-in-aid for scientific research on priority area and grant-in-aid for encouragement of young scientists. This work has been performed under the approval of the Photon Factory Program Advisory Committee (proposal 2001G281).