2020 Fiscal Year Annual Research Report
Atomic-scale analysis of impurity segregated Al2O3 grain boundaries and its physical properties evolution
| Project/Area Number |
20J14631
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| Research Institution | The University of Tokyo |
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Principal Investigator |
楊 楚楚 東京大学, 工学系研究科, 特別研究員(DC2)
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| Project Period (FY) |
2020-04-24 – 2022-03-31
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| Keywords | alumina / grain boundary / segregation / STEM |
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| Outline of Annual Research Achievements |
Small concentrations of dopants that segregate to the grain boundaries can have a profound effect on materials properties. The purpose of this research is to clarify how doping atoms segregate to complex alumina grain boundaries and how they affect the resultant properties.
Firstly, pristine grain boundary has been fabricated by the bicrystal method to precisely control the misorientation and grain boundary structures. Secondly, Ti-diffused grain boundary has been fabricated through heat-treatment of the bicrystal with the Ti film deposited on the surface. Thirdly, with atomic resolution scanning transmission electron microscopy (STEM), the variation of grain boundary structures induced by dopants segregation and the preferred grain boundary segregation sites of dopants have been illustrated, the valence state of dopants has been revealed and the bandgap of pristine and Ti-doped grain boundaries has been clarified.
It was found that Ti dopants preferentially segregated at specific atom sites driven by ionic size mismatch between Ti3+ and Al3+, and the segregation of Ti3+ ions introduces impurity band within the bandgap in Al2O3 grain boundaries. These results provide an in-depth understanding of the local atomic and electronic band structures for Ti-doped grain boundaries.
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| Current Status of Research Progress |
Current Status of Research Progress
2: Research has progressed on the whole more than it was originally planned.
Reason
Bicrystal-based model experiments are extremely powerful and effective for the analysis of atomic structures via electron microscopy and theoretical calculations, which enable us to find out the decisive factors governing the grain boundary segregation and resultant band structures. Our results provide an in-depth understanding of the local atomic and electronic band structures for Ti-doped grain boundaries.
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| Strategy for Future Research Activity |
In the actual cases, doping is usually performed with multiple elements. It has been reported that co-doping can lead to a completely different microstructure, compared with the single doping. These results suggest that there might be interactions between multiple dopants, such as co-segregation and competition, when different dopants exist in grain boundaries of Al2O3. Therefore, it is necessary to clarify the atomic-scale segregation behaviors of multiple dopants at the grain boundaries. In the future study, we will investigate the segregation of multiple doping atoms to the Al2O3 grain boundary, and reveal the interaction mechanism between multiple dopants and the role of segregated atoms in electronic states of grain boundaries.
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