1. St. Petersburg State University, Department
of Crystallography, University Emb. 7/9, 199034 St. Petersburg, Russia
2. Institute of Silicate Chemistry, Russian Academy of Sciences, Makarova Emb.
6, 199034 St. Petersburg, Russia
3. UCCS, Equipe de Chimie du Solide, UMR CNRS 8181, ENSC Lille—UST Lille, BP 90108, 59652 Villeneuve d’Ascq
Cedex, France