Ca4Fe3−xMnxO8−δCl2: A new n=3 Ruddlesden–Popper oxychloride

Solid state solutions of Ca4Fe3−xMnxO8−δCl2 (0.92≤x≤1.79 (δ∼0.1) single crystals were synthesized in CaCl2-flux in air. The structure, determined by single-crystal X-ray diffraction, is related to the n=3 Ruddlesden–Popper phase in space group I4/mmm with strong deviations from the ideal structure. Mn and Fe are disordered over two transition metal sites. Due to the positional disordering of the equatorial oxygen atoms in the MO6 octahedra in Ca4Fe3−xMnxO8−δCl2 both tilting (∼9°) along the c-axis and rotation (∼10.5°) within the ab-plane are observed. All the Fe ions are trivalent, as confirmed by 57Fe Mössbauer spectroscopy and X-ray absorption near edge spectroscopy (XAS), while the formal valence state of Mn varies from very close to 4+ in the x=0.92 to mix-valent 3+/4+ in the x=1.79 member, as indicated by XAS. Magnetic investigations evidence short-range antiferromagnetic ordering already at room temperature and spin-glass behavior at low temperature due to the structural disordering of Mn/Fe.