1Department of Physics and Physical Technologies, Technical University of Clausthal, Leibniz Strasse 4, D-38678 Clausthal-Zellerfeld, Germany
2Gerstenkamp 9, D-51061 Köln, Germany
3Department of Mineralogy and Crystallography, University of Göttingen, Goldschmiedt Strasse 1, D-37077 Göttingen, Germany
4Hamburger Synchrotronstrahlungslabor HASYLAB at Deutsches Elektronen-Synchrotron DESY, Notke Strasse 85, D-22603 Hamburg, Germany