Browsing by Author "Mogare, Kailash M."

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    New ternary and quaternary metal oxides of ruthenium and osmium
    (2006) Mogare, Kailash M.; Jansen, Martin (Prof. Dr. Dr. h. c.)
    Ternary and quaternary oxides of platinum metals are of particular interest because of their intriguing physical, especially magnetic, properties. A very few alkali metal ruthenates and osmates have been reported so far with ruthenium and osmium exhibiting high oxidation states. The scope of the present thesis is to synthesize and characterize new ternary and quaternary alkali metal ruthenates and alkali metal osmates with an acquisition of high oxidation states by the transition metals. To achieve this, high oxygen pressures at elevated temperatures have been applied by using steel autoclaves as reaction vessels. The synthesized alkali metal ruthenates and osmates are investigated qualitatively and quantatively and further characterized using techniques such as powder and single crystal X-ray diffraction, powder neutron diffraction, infra-red/Raman spectroscopy, thermal analysis and measurements of conductivity and magnetic properties. In the case of alkali metal oxo-ruthenates, new hexavalent ruthenates of the compositions A2RuO4 and A3B(RuO4)2 have been explored. Within this family, the compounds display a trend of increasing magnetic interactions with decrease in the size of alkali metals. These interactions are independent from the crystal structure type and can be correlated to the shortest Ru-Ru distances among the Ru6+ ions. Neutron diffraction studies are carried out on Na2RuO4, the ternary oxo-ruthenate displaying the highest magnetic transition temperature in this family, and the low temperature magnetic structure has been deduced from the same. A number of new ternary and quaternary alkali metal oxo-osmates containing heptavalent and octavalent osmium have been explored. Some more high valent osmium containing oxides, which have been predicted and sketchily studied earlier by spectroscopic methods, have now been characterized with their crystal structures and physical properties. Some of the new compounds explored in this work belong to the family of double or triple perovskites (A2BMO6 and A3BM2O9, respectively). Only a few double and triple perovskite oxides with alkali metal cations as the A and B cations are known till today. The new compounds represent the first osmium perovskites containing alkali metal cations at the A site. Sr2CrOsO6, a cubic double perovskite, is re-investigated and found to exhibit the highest Curie temperature known so far in the family of double perovskites. The compound belongs to the increasing list of double perovskites with the task of discovering high ferromagnetic ordering temperature for potential technological applications.