1. Forschungszentrum Jülich GmbH, Institute of Energy and Climate Research, Materials Synthesis and Processing (IEK-1), D-52425 Jülich, Germany
2. Max Planck Institute for Solid State Research, Heisenbergstr. 1, 70569 Stuttgart, Germany
3. University of Twente, Faculty of Science and Technology, Inorganic Membranes, P.O. Box 217, 7500 AE Enschede, The Netherlands