Study of Fe-doped TiO2 and SnO2 by hyperfine techniques and ab initio calculations

L. A. ERRICO

San Pablo, Brasil

Conferencia; Conferencia invitada dictada en el Instituto de Física de la Universidad de San Pablo (USP), Brasil; 2006

Instituto de Física, Universidad de San Pablo

The study of TiO2 and SnO2 semiconducting oxides doped with  transition metals has been a topic of interest in the last years because of its industrial applications, such as catalysts, heat reflecting foils, gas sensors, transparent electrodes, and its potential use in spintronics. There are many experimental and theoretical works done on these R-doped systems (R= Mn, Co, Fe, Ni, Cu, V) mostly focused on the magnetic properties. In the case of the Fe impurity, Mössbauer studies were performed in order to elucidate the hyperfine parameters of Fe substituting Ti or Sn in rutile structure. There are several different data reported for its quadrupole splitting but a unique characterization of Fe hyperfine parameters in this phase has not yet been obtained. Furthermore, several questions remain open concerning the precise location of Fe in the host structure and their hyperfine interaction assignment.  In 2002 we demonstrated the capability of the ab initio full potential linearized augmented plane waves (FP-LAPW) method to predict the hyperfine parameters at impurity sites. Following this approach, we present here a comparison between Mössbauer and FP-LAPW results for the hyperfine parameters at the Fe impurity site in the rutile phase of TiO2 and SnO2. Experimentally, samples of TiO2 and SnO2 powders doped with 7 and 10 at. % of Fe were prepared by mechanical alloying in air. The samples were characterized by X-Ray diffraction, 57Fe Mossbauer spectroscopy, Extended X-ray absorption Fine Structure (EXAFS)  and magnetometric measurements. The FP-LAPW calculations were performed assuming substitutional and interstitial Fe locations and for different impurity concentrations. The effect of oxygen vacancies was also considered.