1. Institute of Energy and Climate Research – Materials Synthesis and Processing (IEK-1) Forschungszentrum Jülich GmbH Jülich 52425 Germany
2. Department of Ceramics and Refractory Materials Institute of Mineral Engineering RWTH Aachen University Aachen 52064 Germany
3. JARA-ENERGY Jülich Aachen Research Alliance Jülich Germany