AgFeOF₂: A Fluorine-Rich Perovskite Oxyfluoride

We synthesized a silver iron oxyfluoride AgFeOF₂ by using a high-pressure reaction. Synchrotron X-ray and neutron diffraction, X-ray absorption, and ⁵⁷Fe Mössbauer spectroscopy indicate that AgFeOF₂ crystallizes in the ideal perovskite structure with iron in a trivalent state, although electron microscopy revealed weak super-reflections. A possible partial ordering in the FeO₂F₄ octahedron is inferred from Mössbauer spectroscopy. The synthesis of the fluorine-rich sample offers an opportunity to study a composition-property relation in AFe^IIIO_3–nF_n (n = 0, 1, and 2). AgFeOF₂ exhibits a G-type antiferromagnetic ordering below T_N ≈ 480 K, which is much lower than the n = 0 and 1 cases, suggesting a weaker superexchange interaction between Fe moments via F 2p orbitals (vs O 2p orbitals).