Impact of Mn3+ upon Structure and Magnetism of the Perovskite Derivative Pb2–xBaxFeMnO5 (x ∼ 0.7)

On the basis of the Mn3+ for Fe3+ substitution in Pb2–xBaxFe2O5, a novel oxide Pb1.3Ba0.7MnFeO5 has been synthesized at normal pressure. Though it belongs to the same structural family, the mixed “MnFe” oxide exhibits a very different structural distortion of its framework compared to the pure “Fe2” oxide, due to the Jahn–Teller effect of Mn3+. Combined neutron diffraction, high resolution electron microscopy/high angle annular dark field–scanning transmission electron microscopy (HAADF–STEM) investigations allow the origin of this difference to be determined. Here we show that the MO6 octahedra of the double perovskite layers in the “MnFe” structure exhibit a strong tetragonal pyramidal distortion “5 + 1”, whereas the “Fe2” structure shows a tetrahedral distortion “4 + 2” of the FeO6 octahedra. Similarly, the MO5 polyhedra of the “MnFe” structure tend toward a tetragonal pyramid, whereas the FeO5 polyhedra of the “Fe2” structure are closer to a trigonal bipyramid. Differently from the oxide Pb2–xBaxFe2O5, which is antiferromagnetic, the oxide Pb1.3Ba0.7MnFeO5 exhibits a spin glass behavior with Tg ∼ 50 K in agreement with the disordered distribution of the Mn3+ and Fe3+ species.