Determination of Fe(IV) species in partially substituted perovskite La_0.6Ca_0.4FeO₃

摘要

The partial substitution for lanthanum in LaFeO₃ perovskite with calcium, a cation with lower oxidation state, causes an electronic unbalance. The X-ray diffraction (XRD) and temperature-programmed reduction (TPR) results suggest that, consequently, the elevation of the iron oxidation state to Fe(IV) occurs. The Mössbauer spectroscopy studies confirm the onset of Fe(IV) to maintain the structure electroneutrality. The quantification of Fe(IV) species is in good agreement with the estimated amount from the hydrogen consumption in the TPR studies. This shows that TPR—a very simple technique widely used to characterize heterogeneous catalysts—is an appropriate technique to quantify Fe(IV) species in LaFeO₃ substituted perovskites. To verify the correct assignment of step corresponding to the Fe(IV) reduction, the different iron species after each reduction step, during the TPR experiment, were confirmed by Mössbauer spectroscopy in controlled atmosphere.