1. CNRS, CEMHTI UPR3079, Univ. Orléans, F-45071 Orléans, France
2. Department of Materials Science (Glass and Ceramics), Friedrich-Alexander-Universität Erlangen-Nürnberg, 91058 Erlangen, Germany
3. Clausthal University of Technology, Institute of Non-Metallic Materials, 38678 Clausthal-Zellerfeld, Germany