Subject Number : S-16-JI-0053
Support Type : Technical support
Proposal Title (English) : Grain boundaries in ZnO ceramics
Username (English) : Juanjuan Xing1)
Affiliation (English) : 1) Materials Genome Institute, Shanghai University

1. Summary
Grain boundary (GB) plays an important role in ZnO ceramics. The nolinearity of I-V curve is ascribed to the GB barriers. However, rare researches were carried out on the systematic analysis of the GBs in ZnO ceramics. To study the GB structures at atomic level as well as GB components would help us understand the microstructural origin of GB barriers better. Our previous results (Tian et al., Acta Mater. 119 (2016) 136−144) show that by introducing defects into multi-doped ZnO ceramics, its thermoelectric performances was greatly enhanced. This is considered due to the generated abundant oxygen vacancies both in the grains and the boudaries.

2. Experimental
Focused ion beam (FIB) was used to prepare thin samples suitable for scanning transmission electron microscope (STEM) observation.
The atomic structures at the grain boundaries of the FIB prepared sample was observed using ARM200F.

3. Results and Discussion
In order to quantitatively measure the distributions of oxygen vacancies, annular bright field (ABF) and high angle annular dark field (HAADF) STEM observations of the multi-doped ZnO ceramic sample, which was sintered in N2+CO atomosphere at 1200℃, were carried out at the GBs. In Fig. 1, the crystal latties for the two adjacent grains were clearly resolved. The inset FFT patterns show that the two grains have different crystal orientations. In Fig. 2, the atoms in the upper grain was visualized, while the lattice of the lower grain is almost invisible due to off zone axis. We haven’t observed any GBs with similar crystal orientations at the two sides, which is necessary for quantitative analysis at the atomic level. Next we will keep trying to obtain better results.

4. Others
A/Prof. Yoshifumi Oshima and Dr. Xiaobin Zhang are acknowledged for their support on STEM observation. Ms Mayu Ito is thanked for her effort in sample preparations. Mr. Koichi Higashimine is also thanked for his helpful discussions in both sample preparation and STEM observation.
5. Publication/Presentation
N/A
6. Patent
N/A