CONICET | Buscador de Institutos y Recursos Humanos

Perovskites of composition La1-xSrxCo1-yFeyO3-d (LSCF) called the attention of the solid oxide fuel cell community due to their good properties as cathode material and their specially interesting mixed conductivity, which increases the cell performace. However, it is well known that different synthesis procedures and treatments change the electronic structure of the material and may improve or, in the worst case, deteriorate the cell transport properties. In this work, we used X-ray Absorption Near Edge Structure (XANES) to study the oxidation state and near environment of Cobalt in nanosized LSCF power sintethized and treated in different ways. La0.4Sr0.6Co0.8Fe0.2O3-d samples were prepared by two different methods called Acetate and HMTA[1], sintered at 900 °C, heat treated in Ar at 500ºC and then heat treated again in O2 at 800ºC. XANES spectra at the Co K-egde were taken from each step using a Si(111) monochromator crystal (Co K-ege=7709 eV) and scanning the energy with 0.1eV steps in the XANES region (D04B XAFS2, LNLS synchrotron facility, Brasil). Shifts in energy and changes of the spectral form, position and intensities of the pre-edge peak and the white line could be observed in the Ar-treated samples. Contrary, the re-oxidized sample did not differe from the non treated samples. The changes observed under reductive atmosphere might be explained by a change in the valece of the Co atoms. This also possibly implies a transformation of some octahedral to tetrahedral environments around the absorbent atom. Because no significant differences were observed between the re-oxidized and the not treated sample, we state the reversibility of this transformation, also detected by X-ray diffraction experiments. This behaviour was observed in the Acetate as well as in the HTMA samples and can be attributed to intrinsec microstructural defects (size and strain) related to these synthesis routes.