Ru-Ru Metal-Metal Bonding in the Chains of Edge-Sharing Octahedra of NdMn1.5Ru0.5O5: A Neutron Powder Diffraction and Magnetic Study

摘要

Four members of a new series of oxides of nominal stoichiometry NdMn2-xRuxO5 (x = 0.1, 0.2, 0.4, 0.5) have been prepared in polycrystalline form by wet.-chemistry procedures followed by thermal treatment at 1000 degrees C. NdMn2-xRuxO5 materials are isostructural with NdMn2O5. Their crystal structures have been refined from XRD data and, for the x = 0.5 oxide, from NPD data in the space group Pbam. The crystal contains infinite chains of (Mn,Ru)O-4+(6), octahedra sharing edges, linked together by dimeric (Mn)O-3+(5) square pyramidal units and NdO8 polyhedra. There is a slight anti-site disordering effect, implying that some Ru cations are introduced at the pyramidal positions, For x = 0.5, the crystallographic formula is Nd+3(Mn0.572(4)4+Ru0.428(4)4+)(oct)(Mn-0.964(8)(3+)-Ru3+ (0.036(8)))(pyr)O-4.92(4). The abrupt contraction of the c axis for x = 0.5, together with the short (Mn,Ru)-(Mn,Ru) distances (2.60 angstrom) observed within the chains of octahedra suggest the presence of Ru-Ru metal bonding for this composition. The magnetic properties are characteristic of spin-glasses, as confirmed by ac susceptibility measurements.