Synthesis, Crystal Structures, and Magnetic Properties of New 12L-Perovskites Ba₄LnRu₃O₁₂ (Ln = Lanthanides)

Synthesis, crystal structures, and magnetic properties of new quaternary oxides Ba 4 LnRu 3 O 12 (Ln = lanthanides) were investigated. From the powder X-ray and neutron diffraction measurements, it is found that they adopt the 12L-perovskite-type structures consisting of Ru 3 O 12 trimers and LnO 6 octahedra. The Ba 4 LnRu 3 O 12 for Ln = Tb−Lu have a hexagonal unit cell with the space group R 3̅ m, while those for Ln = La−Nd, Sm−Gd have a monoclinically distorted cell with C 2/ m . Only for Ln = Ce, Pr, and Tb compounds, the Ln ions are in the tetravalent state. The magnetic properties of these three compounds were investigated. For Ba 4 CeRu 3 O 12, no magnetic transition was observed down to 0.5 K. The Ba 4 PrRu 3 O 12 and Ba 4 TbRu 3 O 12 show an antiferromagnetic transition at 2.4 and 24 K, respectively. The magnetic structure for Ba 4 TbRu 3 O 12 was determined by powder neutron diffraction measurements at low temperatures, which indicates the long-range antiferromagnetic ordering.