Fluorination of perovskite-related phases of composition La1-xSrxFe1-yCoyO3-δ

We report here on the fluorination of the perovskite-related phases La1-xSrxFe1-yCoyO3-delta. The introduction of fluorine in place of oxygen is achieved through a low-temperature (400 degrees C) reaction with poly(vinylidene fluoride). X-ray powder diffraction data show that in all cases the fluorination leads to an expansion in the unit cell, which is consistent with partial replacement of oxygen by fluorine and consequent reduction in the oxidation state of iron and/or cobalt. This reduction in oxidation state is confirmed by X-ray absorption- and Mossbauer-spectroscopy. The Mossbauer spectra show complex magnetically split hyperfine patterns for the fluorinated samples, reflecting the interactions between Fe3+ ions, which are not possible in oxides containing Fe4+. (C) 2008 Elsevier Ltd. All rights reserved.