Mössbauer Effect in the System SrFeO2.5–3.0

Mössbauer spectra were measured at 4°, 78°, and 300°K for the two end members and two intermediate samples of the system SrFeO2.5–3.0. Of primary interest is the spectrum of strontium ferrate (IV) which at 300°K consists of a single unsplit line having a full width at half-intensity of 0.39 mm/sec and an isomer shift relative to copper of —0.171 mm/sec. At 4° and 78°K the spectra consist of six lines with an ISCu of —0.079 mm/sec and an hfs of 331 and 290 kOe, respectively. There is no evidence of quadrupole splitting, consistent with the cubic perovskite structure. The spectra of the pure iron (III) compound are composed of two sets of six-line spectra having ISCu of +0.126 and —0.047 mm/sec and hfs of 489 and 407 kOe, respectively, at 300°K. By analogy with YIG, it was concluded that the structure should contain equivalent amounts of octahedrally and tetrahedrally coordinated iron sites. Subsequent structural analysis confirmed this conclusion and indicated that the phase is isomorphic with brownmillerite. The spectra of the intermediate compounds were found to be more complex and are discussed in terms of accompanying changes in stoichiometry and structure.