131st CEMS Colloquium

Title

Atomic-Scale Dynamics of Grain Boundary Phenomena in Oxides

Abstract

Materials properties of oxides depend on the dynamic behavior under various conditions such as temperature, stress, atmosphere. For example, mechanical properties of poly-crytals are influenced by the interaction of grain boundary (GB), dislocation and crack propagation. On the other hand, oxides processing is often influenced by ion diffusion at high temperatures. So far, many atomic scale observations have been performed for understanding fracture, deformation, diffusion and so on, but these experiments were mostly carried out statically, and the dynamic behavior is still not well understood yet. In addition, these dynamic behaviors often occur at GBs.  In this study, in-situ nanoindentation experiments were conducted for SrTiO₃ and Al₂O₃ bicrystals inside (S)TEM to understand their deformation and fracture process at GBs. For observing ion diffusion along GBs, electron irradiation technique was used to enhance GB migration in Al₂O₃.  Ti-doped Al₂O₃ bicrystals were also used for the ex-situ experiments to in-vestigate atomistic GB diffusion mechanism as a model system.

For observing dislocation-GB interaction, various types of GBs including CSL (Coinci-dence Site Lattice) GBs and low angle tilt and twist GBs for SrTiO₃ and Al₂O₃ were sys-tematically prepared. Various phenomena such as dislocation pile-up at GBs, jog for-mation, jog-drag motion, deformation twinning were dynamically observed by these experiments. The dislocation-GB interaction and its dependence on the GB characters, the propagation mechanism of deformation twinning will be discussed in detail. In addi-tion, the crack propagation behavior of Zr-doped Al₂O₃ GB was directly observed, and the as-fractured wall surfaces were characterized by Cs corrected STEM. It was found that the crack propagated in zigzag manner within the segregated Zr atom layers. The relationship of the atomic-scale crack propagation path and the grain boundary structure will be discussed in detail.

GB migration also plays an important role in considering the sintering behavior and the high temperature mechanical properties in oxides. But, it has been still unclear as to how the GB migration proceeds at atomic scale. Recently, we have found that GB mi-gration behavior in Al₂O₃ can be precisely controlled by the aid of the high-energy elec-tron beam irradiation. We applied this electron beam technique to directly visualize the atomistic GB migration as a stop motion movie. It was revealed that the GB migration is processed by a cooperative shuffling of atoms in GB ledges along specific routes. It is demonstrated that GB migration is facilitated by the GB structural transformations be-tween low-energy GB structures.

References

1. T.Futazuka, R.Ishikawa, N.Shibata and Y. Ikuhara, Nature Commun., 13(1), 5299, (2022).
2. S. Kondo, A. Ishihara, E. Tochigi, N. Shibata, and Y. Ikuhara, Nature Commun., 10, 2112 (2019).
3. J.Wei, B.Feng, R.Ishikawa, T.Yokoi, K.Matsunaga, N.Shibata and Y.Ikuhara, Nat. Mater. 20, 951 (2021).

Contact

email: miho.okada@riken.jp
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