Author(s): Stefania Marin  George Mihail Vlasceanu  Roxana Elena Tiplea  Ioana Raluca Bucur  Madalina Lemnaru  Maria Minodora Marin  Alexandru Mihai Grumezescu Department of Science and Engineering of Oxide Materials and Nanomaterials  Faculty of Applied Chemistry and Materials Science  Politehnica University of Bucharest  Romania