Effect of Fe content on atomic and electronic structure of complex oxides Sr(Ti,Fe)O_{3 − δ}

We present a study of the electronic and atomic structure of two series of SrTi_{1 − x}Fe_xO_{3 − δ} (STFO) powders with different Fe content produced by two different methods, spray pyrolysis or modified Pechini synthesis, by means of soft X-ray absorption spectroscopy. Partial substitution of Ti by Fe atoms in SrTiO₃ were found to cause asymmetric distortion of TiO₆ octahedrons, which increases with increasing Fe content that may violate the cubic symmetry of STFO. The presence mainly of Fe^{3 +} states in octahedral environment at small concentration of Fe atoms along with essentially smaller content of Fe^{4 +} states in octahedral environment where the latter contribution increases with increasing Fe content was traced. It is found that the modified Pechini method allows to synthesize more stable structures but a tendency of the SrO_x formation in the structure prepared by this technique was marked. The spray pyrolysis method gives the structure free of SrO precipitates but the presence of Fe^{3 +} states in tetrahedral environment with Fe content higher than 50% and even a certain amount of Fe^{2 +} ions in an octahedral environment at concentrations higher than 75% in the STFO prepared by this method was established. The O1s (K)-absorption spectra point to increase in oxygen vacancy concentration with increasing Fe content. The lowest degree of structure distortions with enough high oxygen vacancy concentration was traced in STFO (x = 0.25 to x = 0.35) produced by modified Pechini synthesis, which makes it mostly appropriate for technical applications, e.g., as gas sensors, oxygen separation membranes or as fuel cell material.