1. CNR-IOM c/o Institut Laue Langevin, 6 rue J. Horowitz BP156, F-38042 Grenoble, France
2. Laboratoire Léon Brillouin (CEA/CNRS), CEA Saclay, 91191 Gif-sur Yvette Cedex, France
3. National Institute of Standards and Technology, Gaithersburg, Maryland 20899-6102, United States
4. Department of Materials Science and Engineering, University of Maryland, College Park, Maryland 20742, United States
5. Institut Laue Langevin, 6 rue J. Horowitz BP156, F-38042 Grenoble, France
6. Dipartimento di Chimica, Università degli Studi di Perugia, Sezione di Chimica Fisica, via Elce di sotto 8, I-06123 Perugia, Italia