High-Pressure Synthesis, Crystal Structure, and Magnetic Properties of Sr₂MnO₃F: A New Member of Layered Perovskite Oxyfluorides

We have successfully synthesized Sr₂MnO₃F, a new layered perovskite oxyfluoride with a n = 1 Ruddlesden–Popper-type structure using a high-pressure, high-temperature method. Structural refinements against synchrotron X-ray diffraction data collected from manganese oxyfluoride demonstrated that it crystallizes in a tetragonal cell with the space group I4/mmm, in which the Mn cation is located at the octahedral center position. This is in stark contrast to the related oxyhalides that have square-pyramidal coordination such as Sr₂MO₃X (M = Fe, Co, Ni; X = F, Cl) and Sr₂MnO₃Cl. There was no evidence of O/F site order, but close inspection of the anion environment centered at the Mn cation on the basis of bond-valence-sum calculation suggested preferential occupation of the apical sites by the F ion with one oxide ion in a random manner. Magnetic susceptibility and heat capacity measurements revealed an antiferromagnetic ordering at 133 K (=T_N), which is much higher than that of the chloride analogue with corrugated MnO₂ planes (T_N = 80 K).