BaFe_3.39(5)Ru_2.61(5)O₁₁ and BaCo _1.85(6)Ru_4.15(6) O₁₁ · Preparation, crystal structures, and magnetic and transport properties of quaternary transition metal oxoruthenates

Black plate-like single crystals of BaFe_3.39(5)Ru _2.61(5)O₁₁ and BaCo_1.85(6)Ru_4.15(6) O₁₁ were grown from a BaCl₂ flux [hexagonal, space group P6₃/mmc (No. 194), Fe: a = 5.856(1), c = 13.587(1) Å, R1 = 0.029, wR2 = 0.084; Co: a = 5.842(1), c = 13.573(3) Å, R1 = 0.033, wR2 = 0.075]. The crystal structures contain two crystallographic sites with mixed Ru and Fe/Co occupation of different level in octahedral coordination and one site purely occupied by the respective 3d metal. The latter position is in trigonal bipyramidal coordination, with some indication for a displacement of the metal atom towards tetrahedral coordination. According to the charge balance, the ruthenium atoms are incorporated with different electronic situations in the two Ru containing sites. The Co compound may be described as containing Co ²⁺ and Ru⁵⁺ next to Ru³⁺. Magnetic susceptibility data support this assignment. According to magnetization measurements on oriented crystals, BaCO_1.85(6)Ru _4.15(6)O₁₁ is a soft ferromagnetic material with low coercive field and a spontaneous magnetization below T_c = 105 K. It behaves as an electric conductor. However, BaFe_3.39(5)Ru _2.61(5)O₁₁ is a narrow band semiconductor material with ferrimagnetic ordering at T_c = 440 K.