The crystal structure of Ba3CuRu2O9 and comparison to Ba3MRu2O9 (M = In, Co, Ni, and Fe)

The crystal structure of Ba3CuRu2O9, determined by powder neutron diffracti on, is reported for temperatures of 18-295 K. Structural refinements by pow der neutron diffraction for the previously reported compounds Ba3MRu2O9 for M = Fe, Co, Ni, and In are also reported. All structures consist of pairs of face-shared RuO6 octahedra interconnected by corner-sharing MO6 octahedr a. For Ba3Cu Ru2O9, Jahn-Teller distortion of the CuO6 octahedra leads to a n orthorhombic symmetry structure of space group Cmcm with a = 5.6723(1), b = 10.1722(3), and c = 14.1575(3) Angstrom at 295 K. For Ba3FeRu2O9, site o ccupancy disorder is found. Magnetic ordering is observed below 100, 105, a nd 110 K for M = Cu, Ni, and Co, respectively. The magnetic structures at l ow temperatures for M = Co and Ni are described and compared to previous re ports. (C) 1999 Academic Press.