1. 1Department of Chemistry, University of Rome, La Sapienza, Piazzale Aldo Moro 5, I-00185 Roma 34, Italy
2. 2SIMAP Laboratory, ENSEEG/LPTCM, Domaine Universitaire, B. P. 75, F-38402 Saint Martin d'Hères, France
3. 3Materials Science Division, Mail Stop 62B0203, E. O. Lawrence Berkeley National Laboratory, University of California, Berkeley, CA 94720-8253, USA