Atomic structures of Ti‐doped α‐Al₂O₃ Σ13 grain boundary with a small amount of Si impurity

Abstract

Adding a small amount of dopant is an effective way to control grain growth behavior and macroscopic properties in sintered α-Al 2 O 3. For instance, Mg is able to suppress abnormal grain growth, 1-6 Ti promotes grain growth, 7-10 and rare earth elements improve the high-temperature creep resistance. 11-13 Such a small amount of dopants is often concentrated at grain boundaries, 11,14 and it has been claimed that grain boundary atomic structures strongly affect grain growth behavior 15 and also macroscopic properties. 16-18 Therefore, understanding dopant-concentrated grain boundary atomic structures is of fundamental importance. Moreover, in the sintering of α-Al 2 O 3 , it is inevitable to be contaminated by small amounts of unintentional impurities, which intrinsically exist in a raw powder or are introduced during the sintering process via furnaces or the other routes. The cations of Si and Ca are the representative impurities in α-Al 2 O 3 , and the microstructures are strongly affected even with extremely small amounts of

A Review of Grain Boundary and Heterointerface Characterization in Polycrystalline Oxides by (Scanning) Transmission Electron Microscopy

“…For instance, intergranular glassy phases are often observed in sintered ceramics [74,200]. It was elucidated in a work by Ishihara et al [222], that small differences in the amounts of Si impurity led to distinct GB atomic structures in a Ti-doped Σ13 α-Al 2 O 3 GB (Figure 30). In GB type-I, Ti 3+ is replacing Al 3+ while in type-II, Ti 3+ oxidizes to Ti 4+ and the Al vacancies were introduced to the GB to compensate for that leading to three-times larger structure units (oxidation states confirmed by EELS).…”

“…It is evident that there is significant difference between qualitative elemental maps (Figure 31b,d) and quantitative maps (Figure 31e,g) which proves the importance of quantitative analysis. [222] under the terms of the Creative Commons CC BY license.…”

“…All the scale bars are 1 nm. Reprinted from[222] under the terms of the Creative Commons CC BY license.…”