1. Laboratory
of Inorganic Chemistry, Department of Chemistry, University of Helsinki, P.O. Box 55, FI-00014 Helsinki, Finland
2. VTT Technical Research Centre of Finland,
P.O. Box 1000, FI-02044 Espoo, Finland
3. Division
of Materials Physics, Department of Physics, University of Helsinki, P.O. Box 43, FI-00014 Helsinki, Finland