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