AVS 47th International Symposium
    Surface Science Friday Sessions
       Session SS+MC-FrM

Paper SS+MC-FrM3
Controlled Coordination and Oxidation State of Copper and Manganese Cations in Complex Nickel-Copper-Cobalt-Manganese Oxide Thin Films

Friday, October 6, 2000, 9:00 am, Room 209

Session: Characterization of Oxides and Thin Films
Presenter: D.A. KuKuruznyak, University of Washington
Authors: D.A. KuKuruznyak, University of Washington
M.-H. Lee, University of Washington
K.A. Omland, University of Washington
M.C. Gregg, University of Washington
F.S. Ohuchi, University of Washington
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Ionic configuration and cation distribution of the nickel-copper manganite spinels have profound effects on their electrical conduction. As these materials are being widely used for thermistor applications, it is important to find a way of controlling the oxidation states of transition metal cations in these mixed oxides. We have therefore undertaken our research developing a unique method fabricating thermistor composition by chemical solution deposition where cations with unusual coordination and unusual oxidation state can be obtained. Organometallic films deposited on silicon and glass substrates by spin-coating of a liquid precursor solution were decomposed in air at 550°C followed by furnace-annealing at temperatures ranging from 600° to 800°C to obtain single-phase cubic spinel of chemical composition Ni@sub 0.48@Co@sub 0.24@Cu@sub 0.6@Mn@sub 1.68@O@sub 4-x@. XPS, FTIR, and Mossbauer spectroscopy have been used to study oxidation states of transition metal ions. Octahedrally coordinated Cu@super +1@ observed from the specimens (prepared below 700°C) showed unusually large negative binding energy shifts in Cu(2p) peak relative to metallic Cu, of which origin was attributed to the difference in the Madelung potentials. Annealing at higher temperatures causes oxidation of copper to Cu@super 2+@ and reduction of manganese cations from Mn@super 4+@ to Mn@super 3+@. The annealing temperature can precisely control oxidation state distribution of copper and manganese cations.