1. Institute for Inorganic and Analytical Chemistry, Justus-Liebig-University, Heinrich-Buff-Ring 17, D-35392 Giessen, Germany
2. Institute of Materials Research, German Aerospace Center (DLR), D-51170 Cologne, Germany
3. Institute of Experimental Physics I, Justus-Liebig-University, Heinrich-Buff-Ring 16, D-35392 Giessen, Germany
4. Institute for Material Science, Christian-Albrechts-University, Kaiserstrasse 2, D-24143 Kiel, Germany