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Abstract
The oxidation behaviour of Ni nanoparticles at temperatures from 573 to 673 K and the formation process of hollow oxide particles were studied by transmission electron microscopy. In the course of oxidation, a single large void was observed at one site of the interface between inner Ni and outer NiO layer due to vacancy clustering, which occurs during the oxidation process resulting from the rapid outward diffusion of Ni ions through the NiO layer. This suggests that supersaturated vacancies generated at the interface migrate to the site over a long-range distance and aggregate at the site. Ni nanoparticles were fully oxidized to become hollow NiO, in which nano-holes in the form of vacancy clusters were located at the off-centred positions. The de-centring of the voids in hollow NiO is probably due to the large mobility of vacancies inside Ni during oxidation.
1l. (a) 44 567 (1977)
Acknowledgements
One of the authors (R. Nakamura) would like to thank Dr. T. Sakata and Mr. E. Taguchi of The Research Centre for Ultra-High Voltage Electron Microscopy, Osaka University for their technical support in the operation of TEM and FE-SEM. This work was supported by Grant-in-Aid for Scientific Research (No. 17106009) from the Ministry of Education, Culture, Sports, Science and Technology of Japan and also by Research Promotion Grant from the Iron and Steel Institute of Japan.
Notes
1l. (a) 44 567 (1977)