1. Department of Materials Science and Engineering, Yonsei University, 134 Shinchon‐dong, Seodaemoon‐gu, Seoul 120‐749 (Republic of Korea)
2. Chemistry Department, Brookhaven National Laboratory, Upton, NY 11973 (USA)
3. Material Measurement Laboratory, National Institute of Standards and Technology, Gaithersburg, MD 20899 (USA)
4. Energy Efficient Materials Team, Energy & Environmental Division, Korea Institute of Ceramic Engineering & Technology, 233‐5 Gasan‐dong, Guemcheon‐gu, Seoul 153‐801 (Republic of Korea)