INVESTIGATION OF DEFECT ORDERING IN THE PEROVSKITE SYSTEM SRCR0.1FE0.9O3-Y BY MOSSBAUER-SPECTROSCOPY

The oxygen-deficient perovskite system SrCr0.1Fe0.9O3-y has been studied by Mossbauer spectroscopy and X-ray powder diffraction techniques. The material obtained is strongly dependent upon the conditions of preparation. Partially oxidized materials annealed in air and quenched are simple cubic perovskites with considerable cation and oxygen vacancy disorder. Annealing at 1200-degrees-C in vacuo and then cooling step-wise produces an ordered brownmillerite superlattice with the chromium ordered onto octahedral sites. However, rapid cooling gives a microdomain-textured material containing a random distribution of cations; the introduction of chromium stabilizes the high-temperature state of Sr2Fe2O5 which has never been quenched to room temperature. Annealing in an argon stream at 1200-degrees-C gives a partially oxidized crystalline brownmillerite in which the chromium (and extra oxygen) are incorporated in the tetrahedral layers. The magnetic ordering temperatures are correlated with the observed site distribution of the chromium.