Subject Number : S-17-JI-0058
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 methods
Focused ion beam (FIB) was used to prepare thin samples suitable for scanning transmission electron microscope (STEM) observations.

3. Results and Discussions
Since it is difficult to observe the atomic oxygen defects at the both sides near the grain boudary due to different crystal orientations, electron energy loss spectrums (EELS) were used to evaluate the changes of the exist states of oxygen. Multi-doped ZnO ceramic samples, which were sintered in N2+CO atomosphere and air atomosphere at 1200℃ were used. Fig. 1 compares the O-K peaks of the sample annealed in N2+CO atomosphere with the standard one. The experiemental one shows same peak positions with the standard one. Fig. 2 compares the O-K peaks of samples annealled in N2+CO and air, respectively. The shape of the peaks are almost same, only with a shift for about 2 eV. We consider that this is just due to the shift of the zero-loss peak before obtaining the spectrums, rather than an energy shift.

4. Others
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 thanked for his helpful discussions in both sample preparation and STEM observation.

5. Publication/Presentation
N/A

6. Patent
N/A