Fluorination of perovskite-related phases of composition SrFe1-xSnxO3-δ

Perovskite-related compounds of composition SrFe1-xSnxO3-delta (x = 0.31, 0.54) have been prepared. X-ray powder diffraction shows that the materials adopt orthorhombic unit cells. The lattice parameters increase with the incorporation of increasing amounts of tin, which is shown by x-ray absorption near edge structure investigation to be present as Sn4+center dot Fe-57 Mossbauer spectroscopy indicates that iron in these phases is present as Fe5+ and Fe3+ and that the materials adopt the compositions SrFe0.69Sn0.31O2.94 and SrFe0.46Sn0.54O2.88. We propose that the disproportionation of Fe4+ in SrFeO3-delta to Fe5+ and Fe3+ in SrFe1-xSnxO3-delta is driven by the reduction of local lattice strain. The materials have been fluorinated by reaction with poly(vinylidene fluoride) to give products of composition SrFe0.69Sn0.31O2.31F0.69 and SrFe0.46Sn0.54O2.54F0.46. The increased iron to oxygen or fluorine distances as revealed by the extended x-ray absorption fine structure are associated with the reduction of Fe5+ to Fe3+ as evidenced by Fe-57 Mossbauer spectroscopy. The Fe-57 Mossbauer spectra recorded from the fluorinated materials at low temperature show the coexistence of magnetic sextet and non-magnetic doublet components corresponding to networks of Fe3+ coupled through oxide ions. The Sn4+ ions disrupt the coupling and the size of the networks. The magnetic susceptibility measurements and Mossbauer spectra recorded between 4.2 and 300 K are used to model the magnetic properties of these materials, with the larger networks appearing to possess random spin orientations consistent with spin glass-type materials.