Synthesis, Cation Ordering, and Magnetic Properties of the (Sb1 - x Pb x )2(Mn1 - y Sb y )O4 Solid Solutions with the Sb2MnO4-Type Structure

Single phase (Sb1 - x Pb x )2(Mn1 - y Sb y )O4 (0.0 ≤ x ≤ 0.608, 0.0 ≤ y ≤ 0.372) samples with the Sb2MnO4−type structure were prepared at 650 °C by solid-state reaction in evacuated sealed silica tubes. A replacement of Sb by Pb results in the oxidation of Sb3+ to Sb5+, which in turn replaces Mn2+ cations in octahedrally coordinated positions within the infinite rutile-type chains. The crystal structures of Pb0.44Sb1.64Mn0.92O4, Pb0.75Sb1.48Mn0.77O4, Pb1.07Sb1.26Mn0.67O4, and Pb1.186Sb1.175Mn0.639O4 were refined from X-ray powder diffraction data. Increasing the Pb content leads to a decrease of the a parameter from a = 8.719(2) Å to a = 8.6131(8) Å and to an increase of the c parameter from c = 5.999(2) Å to c = 6.2485(7) Å (for Sb2MnO4 and Pb1.216Sb1.155Mn0.628O4, respectively). This occurs due to increasing average cation size at the Pb/Sb position and decreasing cation size at the Mn/Sb position that leads to strong deformation of the (Mn/Sb)O6 octahedra. Starting from the Pb0.75Sb1.48Mn0.77O4 composition a modulated structure with q = γc* was observed by electron diffraction. Hig-resolution electron microscopy observations revealed that Mn and Sb ions order forming layers of octahedrally coordinated positions filled either by Mn2+ or by Sb5+ cations and alternating along the c axis. The dilution of the magnetic Mn2+ cations by nonmagnetic Sb5+ entities leads to a suppression of the antiferromagnetic intrachain interaction and disappearance of long-range magnetic order at high doping level. At T = 20 K the A xy spin component was found to be dominant in the AFM structure of the Pb0.44Sb1.64Mn0.92O4 sample by neutron diffraction.