1. Institute of Glass and Ceramics, Department of Materials Science and Engineering, University of Erlangen—Nuremberg, Martenstrasse 5, DE-91058 Erlangen, Germany
2. CNR-IOM-OGG c/o ESRF − The European Synchrotron, LISA CRG, 71 Avenue des Martyrs, CS 40220, F-38043 Grenoble, France