Assessment of the optimum degree of Sr3Fe2MoO9 electron-doping through oxygen removal: An X-ray powder diffraction and 57Fe Mössbauer spectroscopy study

We describe the preparation and structural characterization by X-ray powder diffraction (XRPD) and Mössbauer spectroscopy of three electron-doped perovskites Sr3Fe2MoO9−δ with Fe/Mo = 2 obtained from Sr3Fe2MoO9. The compounds were synthesized by topotactic reduction with H2/N2 (5/95) at 600, 700 and 800 °C. Above 800 °C the Fe/Mo ratio changes from Fe/Mo = 2-1 < Fe/Mo < 2. The structural refinements of the XRPD data for the reduced perovskites were carried out by the Rietveld profile analysis method. The crystal structure of these phases is cubic, space group Fm3¯m, with cationic disorder at the two different B sites that can be populated in variable proportions by the Fe atoms. The Mössbauer spectra allowed determining the evolution of the different species formed after the treatments at different temperatures and confirm that Fe ions in the samples reduced at 600, 700 and 800 °C are only in the high-spin Fe3+ electronic state.