1. Department of Thermoelectric Materials and Systems, Institute of Materials Research, German Aerospace Center, 51147 Cologne, Germany
2. Institute of Inorganic and Analytical Chemistry, JLU Giessen, 35390 Giessen, Germany
3. Institute of Technology for Nanostructures (NST) and CENIDE, Faculty of Engineering, University of Duisburg-Essen, 47057 Duisburg, Germany