Electron spin resonance and x-ray photoelectron spectroscopic studies on an electrochemically deposited film of mixed ma
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A thin film of mixed manganese and vanadium oxides was formed on a platinum electrode by electro-oxidation of Mn2+ precursors in aqueous solution with VO3−. X-ray analysis revealed that the film consists of an amorphous phase including trivalent and tetravalent Mn ions. The infrared spectrum exhibited the bands attributable to V2O5, suggesting that protonation and dehydration of VO3− occur to form the polymeric structure. The mixed oxide film showed no electron spin resonance signal in an as-deposited state. After the film-coated electrode was immersed into water and then dehydrated, however, a characteristic signal (g ⳱ 2.022) of Mn2+ in the solid phase appeared, accompanying a decrease in the vanadium content. This suggests that Mn3+ ions not in the oxide network, but pairing with unreacted VO3−, are disproportionated to MnO and MnO2 by the reaction with water, while the VO3− is diffused to keep the charge valance of the film.
I. INTRODUCTION
Manganese oxides are of particular interest because they readily intercalate lithium ions into their structures and are therefore potentially useful as cathodes in lithium secondary batteries. Although the spinel-type oxide was studied most extensively, the amorphous one has attracted increasing attention in the last few years.1,2 This is because amorphous materials generally provide higher specific capacities than their crystalline counterparts. Besides, the incorporation of other transition metals into the host structure is a common strategy for improving cycling performance and rate capability.3,4 Hence, the method for preparing such mixed oxides with a thin film form is required in relation to application for microelectronic devices. Oxide/hydroxide films of transition metals have been fabricated by various techniques including sputtering, chemical vapor deposition, sol-gel coating, and recently by electrochemical deposition. The last method, which gives low environmental loading and produces materials at low cost, is suitable for preparing thin and uniform films on complicated substrates with a high degree of reproducibility. Nevertheless, compared to the practical applications of metal oxide films, much less attention is devoted to the preparation and characterization of them. Thus, the films prepared by room temperature or
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J. Mater. Res., Vol. 18, No. 10, Oct 2003 Downloaded: 03 Apr 2015
low temperature techniques were heat treated very often to be converted to the thermodynamically stable structure, and very little attention was given to the spectroscopic properties of the as-synthesized materials. This paper reports a new electrochemical route for preparing amorphous thin films of mixed manganese and vanadium oxides, which is constituted by electrolyzing Mn2+ precursors in aqueous solution containing VO3−. The resulting films were characterized by field emission scanning electron spectroscopy (FE-SEM), electron probe microanalysis (EPMA), Fourier-
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