SYNTHESIS UNDER HIGH-PRESSURE AND CHARACTERIZATION BY MOSSBAUER-SPECTROSCOPY OF NONSTOICHIOMETRIC CA2FE2O5.12

The calcium iron oxide Ca2Fe2O5 which contains alternate layers of iron-oxygen octahedra and tetrahedra has been found to take up additional oxygen under high pressure and elevated temperature. The Mossbauer spectra in the range 4.2-290 K establish that all the original material has been transformed into a new phase which is still structurally related to the original lattice, but features a disordered introduction of oxygen into the tetrahedral layers and oxidation of some of the iron to the +4 oxidation state. At least six distinct iron sites can be identified, and the coordination numbers established. The structural relationship of these sites and the magnetic characteristics are discussed.