Preparação e caracterização de TiO2:Co:Sb nanoestruturado

Abstract

The interest in transitional metal doped oxides has been grown very fast in the last years since the theoretical prediction of room temperature ferromagnetism for such kind of systems. However, in spite of the great number of experimental and theoretical reports in this research area, the nature of the often observed magnetic properties still remain a controversial issue. Several recent works has been shown that ferromagnetic ordering depends on structural defects. Our recent experimental results demonstrates that defects at the anion sites (oxygen) are not effective to promote the desired ferromagnetism. In this context, we propose here the study related to the synthesis and the structural and magnetic characterization of oxide samples based on the nanostructured anatase TiO2 matrix doped with Co and Sb. The purpose of the co-doping with Sb is to introduce defects at the Ti due the process of charge compensation associated to the differences in the states of oxidation. In this work we prepared nanostructured anatase Ti1-x-yCoxSbyO2-δ samples with x = 0; 0.03 and y = 0.04; 0.08; 0.12; and 0.16. The samples were prepared by the Pechini method. The structural characterization were conducted by X-ray diffraction, Raman scattering spectroscopy, X-ray absorption and high-resolution transmission electron microscopy. The granulometry is lower than 10 nm. The structural data confirms the Co and the Sb incorporation into the anatase TiO2 matrix with no segregated related phases. With the Sb co-doping the structure of the samples are gradually degraded. X-ray absorption results reveals the presence of Sb3+ and Sb5+ in the samples and an induced growing concentration of both O and Ti vacancies. The magnetic characterization were conducted by using a SQUID magnetometer. The results present a room temperature ferromagnetic phase for all the samples closely related to the concentration of Ti vacancies.