Magnetic and electrical properties of quadruple perovskites with 12 layer structures Ba4LnM3O12 (Ln=rare earths; M=Ru, Ir): The role of metal–metal bonding in perovskite-related oxides

Structures and magnetic and electrical properties of quadruple perovskites containing rare earths Ba4LnM 3O12 (Ln =rare earths; M =Ru, Ir) were investigated. They crystallize in the 12L-perovskite-type structure. Three M O6 octahedra are connected to each other by face-sharing and form a M 3O12 trimer. The M 3O12 trimers and Ln O6 octahedra are alternately linked by corner-sharing, forming the perovskite-type structure with 12 layers. For Ln =Ce, Pr, and Tb, both the Ln and M ions are in the tetravalent state (Ba4Ln 4+M 4+3O12), and for other Ln ions, Ln ions are in the trivalent state and the mean oxidation state of M ions is +4.33 (Ba4Ln 3+M 4.33+3O12). All the Ba4Ln 3+Ru4.33+3O12 compounds show magnetic ordering at low temperatures, while any of the corresponding iridium-containing compounds Ba4Ln 3+Ir4.33+3O12 is paramagnetic down to 1.8 K. Ba4Ce4+Ir4+3O12 orders antiferromagnetically at 10.5 K, while the corresponding ruthenium-containing compound Ba4Ce4+Ru4+3O12 is paramagnetic. These magnetic results were well understood by the magnetic behavior of M 3O12. The effective magnetic moments and the entropy change for the magnetic ordering show that the trimers Ru4.33+3O12 and Ir4+3O12 have the S =View the MathML source12 ground state, and in other cases there is no magnetic contribution from the trimers Ru4+3O12 or Ir4.33+3O12. Measurements of the electrical resistivity of Ba4LnM3O12 and its analysis show that these compounds demonstrate two-dimensional Mott-variable range hopping behavior.