Synthesis and Characterization of SrFe_<i>x</i>Mn_1–<i>x</i>(O,F)_3−δ Oxide (δ = 0 and 0.5) and Oxyfluoride Perovskite Films

Abstract

We report the synthesis and characterization of as-grown SrFe_<i>x</i>Mn_1-<i>x</i>O_2.5 epitaxial films, which were also subjected to postgrowth oxidation and topotactic fluorination to obtain SrFe_<i>x</i>Mn_1-<i>x</i>O₃ and SrFe_<i>x</i>Mn_1-<i>x</i>O_2.5-δF_γ films. We show how both the B-site cation and anion composition influence the structural, electronic, and optical properties of this family of perovskite materials. The Fe substitution of Mn in SrMnO_2.5 gradually expands the <i>c</i>-axis parameter, as indicated by X-ray diffraction. With increasing <i>x</i>, the F content incorporated under identical fluorination conditions increases, reaching its maximum in SrFeO_2.5-δF_γ. In the compounds with mixed B-site occupation, the Fe 2p photoemission peaks are shifted upon fluorination, while the Mn 2p peaks are not, suggesting inductive effects lead to asymmetric responses in how F alters the Mn and Fe bonds. Electronic transport measurements reveal all compounds are insulators, with the exception of SrFeO₃, and demonstrate that fluorination increases resistivity for all values of <i>x</i>. Optical absorption spectra in the SrFe_<i>x</i>Mn_1-<i>x</i>O_2.5 and SrFe_<i>x</i>Mn_1-<i>x</i>O₃ films evolve systematically as a function of <i>x</i>, consistent with a physical scenario in which optical changes with Fe substitution arise from a linear combination of Mn and Fe 3d bands within the electronic structure. In contrast, the F incorporation induces nonlinear changes to the optical response, suggesting a more complex impact on the electronic structure in materials with concurrent B-site and anion site substitution.