Ciobanu, Carmen Steluta, National Institute of Materials Physics, P.O. Box MG 07, 07725, Magurele and University Politehnica of Bucharest, Faculty of Applied Chemistry and Materials Science, Department of Science and Engineering of Oxide Materials and Nanomaterials, 1-7 Polizu Street, P.O. Box 12-134, 011061 Bucharest, Romania