Advanced In Situ (S)TEM for Grain Boundary Phenomena in Oxides

Oxides have been widely used for structural applications because of their superior mechanical properties. It has been known that the behavior of GB properties is strongly dependent on the GB characters such as misorientation angle between two adjacent crystals and GB plane, however, such effect has not been clarified yet. In addition, this effect is much influenced by the dopant segregation at GBs in oxides. In this study, in order to clarify the GB atomic structures in oxides such as Al₂O₃, ZrO₂, SrTiO₃, their bicrystals including various types of GBs with and without dopants were systematically fabricated. Then, the atomic structures and chemistry in thus fabricated GBs were characterized by aberration corrected STEM (scanning transmission electron microscopy), atom-resolved EDS and EELS, and the relationship between GB characters, segregated dopants and the properties for such ceramics will be discussed.<br/>GB dynamics such as fracture and migration also play an important role in considering the sintering behavior and the properties. However, it has been still unclear as to how the GB fractures and migration proceeds at atomic scale. In this study, GB fracture and deformation are dynamically observed by TEM in-situ straining experiments using nano-indentation and newly developed MEMS straining holder. It was found that GB fracture occurs along the special crystal plane and dislocations are emitted from the crack front. Recently, we have proposed that GB migration behavior in ceramics can be precisely controlled by the aid of the high-energy electron beam irradiation. This electron beam technique was applied to directly visualize the atomistic GB migration. It was revealed that the GB migration is processed by a cooperative shuffling of atoms in GB ledges along specific routes. As a result, the GB passed through several different GB structures with low formation energies during GB migration.<br/><br/>References<br/>[1] S. Kondo, T. Mitsuma, N. Shibata, Y. Ikuhara, Sci. Adv., 2[11], e1501926 (2016).<br/>[2] S. Kondo, A. Ishihara, E. Tochigi, N. Shibata, and Y. Ikuhara, Nature Commun., 10, 2112 (2019).<br/>[3] J.Wei, B.Feng, R.Ishikawa, T.Yokoi, K.Matsunaga, N.Shibata and Y.Ikuhara, Nat. Mater. 20, 951 (2021).<br/>[4] J.Wei, B.Feng, E.Tochigi, N.Shibata and Y.Ikuhara, Nat. Commun., 13, 1455 (2022).<br/>[5] S. Kobayashi, A. Kuwabara, C. A.J. Fisher, Y. Ukyo and Y. Ikuhara, Nat. Commun., 9, 2863 (2018).