1. Institute for Materials Research, Tohoku University, Katahira, Aoba-ku, Sendai 980-8577
2. Superconductivity Research Laboratory, International Superconductivity Technology Center, Koto-ku, Tokyo 135-0062
3. Department of Chemistry, Graduate School of Science, Kyoto University, Kyoto 606-8502
4. Advanced Science Research Center, Japan Atomic Energy Research Institute, Tokai, Ibaraki 319-1195