【公開日：2024.07.25】【最終更新日：2024.05.29】
課題データ / Project Data
課題番号 / Project Issue Number
23UT0054
利用課題名 / Title
Investigating Dopant Diffusion and Segregation in Grain Boundaries: A Study on Behaviors and Mechanisms
利用した実施機関 / Support Institute
東京大学 / Tokyo Univ.
機関外・機関内の利用 / External or Internal Use
内部利用（ARIM事業参画者以外）/Internal Use (by non ARIM members)
技術領域 / Technology Area
【横断技術領域 / Cross-Technology Area】（主 / Main）計測・分析/Advanced Characterization（副 / Sub）-
【重要技術領域 / Important Technology Area】（主 / Main）高度なデバイス機能の発現を可能とするマテリアル/Materials allowing high-level device functions to be performed（副 / Sub）次世代ナノスケールマテリアル/Next-generation nanoscale materials
キーワード / Keywords
電子顕微鏡/ Electronic microscope,セラミックスデバイス/ Ceramic device,原子層薄膜/ Atomic layer thin film
利用者と利用形態 / User and Support Type
利用者名（課題申請者）/ User Name (Project Applicant)
YANG CHUCHU
所属名 / Affiliation
東京大学 工学系研究科 総合研究機構
共同利用者氏名 / Names of Collaborators in Other Institutes Than Hub and Spoke Institutes
ARIM実施機関支援担当者 / Names of Collaborators in The Hub and Spoke Institutes
Ayumi Kimura
利用形態 / Support Type
（主 / Main）機器利用/Equipment Utilization（副 / Sub）-
利用した主な設備 / Equipment Used in This Project
報告書データ / Report
概要（目的・用途・実施内容）/ Abstract (Aim, Use Applications and Contents)
Alumina ceramics (α-Al2O3) are widely used as high-temperature structural materials due to their high mechanical strength, thermal stability and electrical insulation. These properties are strongly influenced by grain boundaries (GBs). Impurity or dopant diffusion along the gain boundaries plays an important role in regulating the properties of Al2O3. Moreover, GBs serve as preferential segregation sinks for dopants. Thus, it is important to understand dopant diffusion and segregation behaviors along GBs. In this study, the GB structures before and after different dopants diffusion were characterized by transmission electron microscopy (TEM) and atomic-resolution scanning TEM (STEM), and dopant segregation behaviors were investigated at the atomic level.
実験 / Experimental
An Al2O3 bicrystal with Σ7 GB was fabricated by bonding two single crystals (>99.99%) at 1500 °C for 10 h in air. The Ca/Si-doped GB was fabricated by annealing the undoped bicrystal sample at a reducing atmosphere (1400°C, 10h, 97% Ar + 3% H2 atmosphere) in the furnace tube (SSA-S) containing impurities of Ca and Si. During annealing, Ca and Si impurities prefer to diffuse along GBs. The formation of Ca/Si co-segregated GB was confirmed, but only at the region in close vicinity to the surface of the bicrystal. To obtain Ti-doped and Ti/Ca/Si-doped samples, we deposited the Ti film on the (0001) surface of the bicrystal by a vacuum evaporator. Subsequently, the samples were annealed in the same furnace with the same annealing condition, so that Ti, Ca and Si will diffuse into the GBs. While Ti/Ca/Si-doped samples can be obtained only at the position close to the surface, Ti-doped GBs can be obtained at the position far from the surface. The GBs after dopant diffusion were characterized by TEM images and selected area electron diffraction (JEM-2100HC, JEOL, 200kV). Furthermore, the GB atomic structures were characterized by STEM (JEM-ARM200F, JEOL, 200kV), and elemental analysis was performed by energy dispersive X-ray spectroscopy (EDS).
結果と考察 / Results and Discussion
High angle annular dark field (HAADF) STEM observations show that the pristine GB consists of a six-membered ring and a four-membered ring, while Ca/Si-doped and Ti/Ca/Si-doped GBs show a GB structure with seven-membered ring and a five-membered ring. The dopant segregation has induced a GB structural transformation in the Σ7 GB, however, the framework of GB structure does not change with the dopants species. The distributions of these dopants in the GBs were further revealed by the atomic-scale EDS mapping. It is demonstrated that Ti and Ca/Si segregate at some specific Al atom sites in the Ti-doped and Ca/Si-doped GBs, respectively. However, the segregation sites for Ti have changed drastically in the Ti/Ca/Si-doped sample compared with Ti-doped GB, indicating that interactions between the Ti and Ca dopants occurred during segregation. In combination with density functional theory calculations on the segregation energies, it suggests that Ca and Si are synergistically co-segregated in Ca/Si-doped and Ti/Ca/Si-doped GBs, maintaining charge neutrality within the GB core, while the site competition between Ca and Ti occurs in the Ti/Ca/Si-doped GB. Furthermore, valence EELS measurements reveal that the electronic states of the segregated dopants govern the GB band gap, which is little affected by the interactions between different elements. These findings provide in-depth understanding of the segregation mechanisms of dopant interactions between different elements in the GBs.
図・表・数式 / Figures, Tables and Equations
その他・特記事項（参考文献・謝辞等） / Remarks(References and Acknowledgements)
This work was partly supported by Grant-in-Aid for Scientific
Research (S) (JP22H04960), Grant-in-Aid for Scientific Research on Innovative
Areas (JP19H05788) and Grants-in-Aid for Early-Career Scientists (JP22K14463)
from the Japan Society for the Promotion of Science (JSPS).
DOI：10.2109/jcersj2.23054
URL：http://dx.doi.org/10.2109/jcersj2.23054
発表年：2023
タイトル：The effect of annealing atmospheres on the segregation behaviors in Ti-doped α-Al2O3 grain boundary
筆頭著者：Chuchu Yang
ジャーナルタイトル：Journal of the Ceramic Society of Japan
ボリューム：131
ページ：608-612
成果発表・成果利用 / Publication and Patents
論文・プロシーディング（DOIのあるもの） / DOI (Publication and Proceedings)
-
Chuchu Yang, The atomic and electronic band structures in Ca/Si-doped and Ca/Si/Ti-doped Al2O3 grain boundaries, Journal of the European Ceramic Society, 44, 1005-1011(2024).
DOI: 10.1016/j.jeurceramsoc.2023.09.011
-
Chuchu Yang, Dopant-impurity interactions on grain boundary segregation in alumina, Journal of Materials Science & Technology, 181, 58-62(2024).
DOI: 10.1016/j.jmst.2023.08.066
口頭発表、ポスター発表および、その他の論文 / Oral Presentations etc.
- 1. C.C. Yang, B. Feng, N. Shibata, Y. Ikuhara. “Atomistic segregation behaviors of Ti dopants in Al2O3 grain boundaries”, Advanced Materials Research Grand Meeting (MRM2023/IUMRS-ICA2023), Kyoto, Japan, December 11, 2023. (Oral presentation)
- 2. C.C. Yang, B. Feng, N. Shibata, Y. Ikuhara. “Revealing atomistic dopant segregation behaviors in Al2O3 grain boundaries”, The 20th International Microscopy Congress (IMC20), Busan, Korea, September 11, 2023. (Oral presentation)
- 4. C.C. Yang, B. Feng, N. Shibata, Y. Ikuhara. “Atomic-scale Ti segregation behaviors in Al2O3 grain boundaries”, The 79th Annual Meeting of The Japanese Society of Microscopy, Matsue, Japan, June 28, 2023. (Oral presentation)
- 5. C.C. Yang, B. Feng, N. Shibata, Y. Ikuhara. “Atomic structures and Ti segregation behaviors in Al2O3 grain boundaries”, International Workshop on Advanced and In Situ Microscopies of Functional Nanomaterials and Devices (IAMNano), Matsue, Japan, June 28, 2023. (Poster presentation)
特許 / Patents
特許出願件数 / Number of Patent Applications：0件
特許登録件数 / Number of Registered Patents：0件