1. Superconductivity Laboratory, FSN-COND, ENEA, Via E. Fermi 45, 00044 Frascati (Rome), Italy
2. Department of Chemical Sciences and Technologies, Via della Ricerca Scientifica, Tor Vergata University, Rome 000173, Italy
3. Central Facility for Electron Microscopy, RWTH Aachen University, Ahornstraße 55, 52074 Aachen, Germany