A STUDY OF MICRODOMAIN FORMATION AND STRUCTURAL INTERGROWTH IN THE OXYGEN-DEFICIENT PEROVSKITE CA2FE2-XCRXO5+Y BY MOSSBAUER-SPECTROSCOPY

The oxygen-deficient perovskite system Ca2Fe2-xCrxO5+y (x = 0.5, 0.67, 1.0) has been studied by Mössbauer spectroscopy and X-ray powder diffraction techniques. The nature of the material obtained depends strongly upon the conditions of preparation, although the iron is always present as Fe3+. Complete reduction (y = 0) can be achieved in vacuo for x < 0.56 to give a single-phase brownmillerite containing Cr3+ fully ordered onto the octahedral sites. At higher chromium content a three-phase product is obtained. Preparations in air are strongly oxidized, with the exsolution of Cr5+ in Ca3Cr2O8 (or Cr6+ in CaCrO4) below 1200°C. Above this temperature the Cr is incorporated into a perovskite-related lattice as Cr4+. There is evidence for microdomain formation with Cr4+ concentrating in the domain walls, and for structural intergrowth of the A2B2O5 brownmillerite and A3B3O8 lattices. © 1990.