1. Department of Materials and Earth Sciences Nonmetallic Inorganic Materials Technical University of Darmstadt Alarich‐Weiss‐Straße 2 64287 Darmstadt Germany
2. Department of Materials Science and Engineering Iowa State University Ames IA 50011 USA
3. Institute for Chemistry and Technology of Materials Graz University of Technology Stremayrgasse 9 Graz 8010 Austria