1. Max-Planck Institute for Chemical Physics of Solids; Nöthnitzer Straße 40 Dresden 01187 Germany
2. Department of Physics and Earth Sciences; Parma University; Viale G.P., Usberti n.7/A (Parco Area delle Scienze) 43124 Parma Italy
3. IMEM-CNR; Parco Area delle Scienze 37/A 43124 Parma Italy