NaFe3(HPO3)2((H,F)PO2OH)6: A Potential Cathode Material and a Novel Ferrimagnet.

A novel iron fluorophosphite, NaFe3(HPO3)2((H,F)PO2OH)6, was synthesized by a dry low-temperature synthesis route. The phase was shown to be electrochemically active for reversible insertion of Na(+) ions, with an average discharge voltage of 2.5 V and an experimental capacity at low rates of up to 90 mAhg(-1). Simple synthesis, low-cost materials, excellent capacity retention, and efficiency suggest this class of material is competitive with similar oxyanion-based compounds as a cathode material for Na batteries. The characterization of physical properties by means of magnetization, specific heat, and electron spin resonance measurements confirms the presence of two magnetically nonequivalent Fe(3+) sites. The compound orders magnetically at TC ≈ 9.4 K into a state with spontaneous magnetization.

Na2MoO(2-δ)F(4+δ)--a perovskite with a unique combination of atomic orderings and octahedral tilts.

Na2MoO2-δF4+δ (δ ∼ 0.08) displays a unique variant of the perovskite structure, with simultaneous (Na,vacancy) ordering on the A-site, (Na,Mo) ordering on the B-site, (O,F) ordering on the anion site and an unusual NaNbO3-like octahedral tilt system.