Staged fluorine insertion into manganese oxides with Ruddlesden-Popper structures: LaSrMnO4F and La1.2Sr1.8Mn2O7F

The synthesis, structures and magnetic properties of two fluorine-intercalated layered manganates, LaSrMnO₄F and La_1.2Sr_1.8Mn₂O₇F, are reported. Rietveld structure refinement based on time of flight neutron powder diffraction data indicates that both compounds are tetragonal (space group P4/nmm) with cell parameters a = 3.77696(7) Å, c = 14.1026(8) Å (LaSrMnO₄F) and a = 3.8103(1) Å, c = 21.7220(2) Å (La_1.2Sr_1.8Mn₂O₇F). Fluorine occupies interstitial sites in only one of the two rock salt layers available in the unit cell, leading to novel staged intercalation structures. The interstitial fluorine increases the spacing between the two adjacent rock salt layers and thereby causes a significant reduction in the Mn-O apical bonds directed towards the intercalated regions. The Mn valences of both compounds are close to 4+, and no long range magnetic order was observed in the title compounds down to 5 K.