Crystal structures and magnetic properties of dimorphic Li3OsO4

Rocksalt-type oxides Li3OsO4 with disordered and ordered arrangements of Li and Os were synthesized. The disordered phase crystallizes in the ideal rocksalt structure with cubic space group Fm3m , while the ordered polymorph adopts the monoclinic Na3BiO4-type structure (space group P2/c). The analyses of X-ray and neutron diffraction data of monoclinic Li3OsO4 indicate that there is a considerable anti-site disorder of Li and Os and that the sample is nonstoichiometric [Li3.045(5)Os0.955(5)O4]. In monoclinic Li3OsO4 the OsO6 octahedra are not isolated from each other but they form edge-sharing zigzag chains. Both cubic and monoclinic Li3OsO4 are electrically semiconducting. Cubic Li3OsO4 does not show any sign of magnetic order down to 2 K, whereas the chi(T) data of monoclinic Li3OsO4 display an anomaly at 310 K. However, the neutron diffraction study indicated no evidence of long-range magnetic order. The anomaly at 310 K may be caused by short-range antiferromagnetic ordering within the individual Os chains.