1. Department of Materials Science and Engineering, Yonsei University, 50 Yonsei-ro, Seodaemun-gu, Seoul 120-749, South Korea
2. R&D Center, Chang Sung Co. Ltd., 11-9, Namdong Industrial Area, Namdong-gu, Incheon 405-100, South Korea
3. Future Convergence Ceramic Division, Korea Institute of Ceramic Engineering and Technology, Seoul 153-801, South Korea