1. Contribution from the National Creative Research Initiative Center for Oxide Nanocrystalline Materials and School of Chemical Engineering, Seoul National University, Seoul 151-744, Korea, School of Materials Science and Engineering, Seoul National University, Seoul 151-744, Korea, New Material Evaluation Center, Korea Research Institute of Standards and Science, Taeduk Science Town, P.O. Box 102, Taejon 305-600, Korea, and Department of Chemistry, University of California, Santa Cruz, California 95064