Structural and Mössbauer study of Sr2FeO3X (X = F, Cl, Br) and the magnetic structure of Sr2FeO3F

The structures of Sr2FeO3F, Sr2FeO3Cl and Sr2FeO3Br have been investigated using powder neutron diffraction (PND). All three ferrates crystallise in the primitive tetragonal space group P4/nmm and the anions are fully ordered giving iron oxygen square pyramids separated by rock salt type layers of strontium halide. 57Fe Mössbauer data have been collected and confirm one iron(III) site of distorted octahedral geometry in all three structures. Variable temperature PND data have been used to determine the √2a × 2c magnetic superstructure of Sr2FeO3F.