1. Powder & Ceramics Division, Korea Institute of Materials Science, Changwon, Gyeongnam 642-831, South Korea
2. Research Center for Ultra-High Voltage Electron Microscopy, Osaka University, Ibaraki, Osaka 567-0047, Japan
3. Division of Materials and Manufacturing Science, Graduate School of Engineering, Osaka University, Suita, Osaka 565-0871, Japan