Structure-property relationships in oxides containing select platinum group metals Public Deposited

http://ir.library.oregonstate.edu/concern/graduate_thesis_or_dissertations/pc289m30r

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  • Oxide materials exhibit a wide variety of structures and properties. In particular, transition metal oxides tend to be highly stable while exhibiting a wide range of properties that can be used for numerous applications. This work focuses on investigating how the structures’ of 4d and 5d transition metal oxides influences their properties. Specifically oxides of Ru, Rh and Ir were investigated. A complete solid solution was found between isostructural Pb₃Mn₇O₁₅ and Pb₃Rh₇O₁₅. Pb₃Rh₇O₁₅ shows a Verwey-type transition at 185 K. This transition remains with a 3 % substitution of Mn for Rh but disappears with a 4 % substitution of Mn for Rh. The structure was found to expand in the direction perpendicular to the layers of the structure, which is the c-axis, despite a contracting unit cell. Bi for Pb substitution in Pb₃Mn₇O₁₅ was found to be limited as compared to in Pb₃Rh₇O₁₅. Alkali metal substitution on the A-site of the orthorhombic perovskite SrRuO₃ showed only low substitution levels were possible. Nonetheless, the substituted phases showed decreased ferromagnetic Curie temperatures, increased electrical resisitivity and relatively unchanged Seebeck coefficients. Thermoelectric studies of Sr[subscript 2-x]La[subscript x]CoRuO₆ perovskite phases showed Sr₁.₁La₀.₉CoRuO₆ with the best thermoelectric performance. This system showed possible correlations between cation ordering on the B-site and the charge carrier transport. A similar thermoelectric study of (RhV)[subscript 1+x]Ti[subscript 1-2x]O₆ phases crystallizing in a disordered trirutile structure was done. Electron carriers were found to be dominant and dependent on Ti content. The electron carriers appear to become diminished at higher temperatures. Sr₂IrO₄ crystallizes in a K₂NiF₄-type structure. Effects of Ti, Fe and Co substitution for Ir were investigated. A complete Sr₂Ir[subscript 1-x]Ti[subscript x]O₄ solid solution was synthesized and characterized while limited solubility was found for Fe and Co substitutions. All substitutions showed a decrease in the c-cell parameter coupled with a decrease in octahedral tilting. All substitutions also showed a decrease in magnetic susceptibility and an increase in the paramagnetic effective moment was observed for Co and Fe doped samples. An incomplete solid solution was formed for Sr₂Ti[subscript 1-x]Rh[subscript x]O₄ phases; however effects of increased octahedral tilting with higher Rh content were observed.
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