Synthesis, structural and magnetic characterisation of the fluorinated compound 15R-BaFeO₂F

The compounds 15R-BaFeO2F and 15R-BaFeO2.27F0.5 have been synthesised by the low temperature fluorination of 15R-BaFeO3−dF0.2 using polyvinylidenedifluoride (PVDF) as a fluorination agent. The materials have been structurally characterised by Rietveld analysis of the X-ray- and HRPD-powder neutron diffraction data. A detailed analysis of bond valence sums suggests that the oxide and fluoride ions order on the different anion sites. A reinvestigation of our recently published structure (Clemens et al., 2013) [34] of 6H-BaFeO2F is also reported and incorporation of fluoride in h-type layers is also confirmed in this compound. The magnetic moments for 15R-BaFeO2F and 15R-BaFeO2.25F0.5 align in the a/b-plane with antiferromagnetic alignment of the moments between adjacent layers, and are flipped by 90° as compared to the precursor compound. 15R-BaFeO2F exhibits very robust antiferromagnetism with a Néel temperature between 300 and 400 °C.