The metals chemical states in hydrated vanadium oxides

Sigitas Mickevicius 1Vladimir Bondarenka 1Sergej Grebinskij 1Henrikas Tvardauskas 1Sigitas Tamulevicius 2Mindaugas Andrulevicius 2

1. Semiconductor Physics Institute, A.Gostauto 11, Vilnius LT-2600, Lithuania
2. Kaunas University of Technology, Institute of Physical Electronics, Savanoriu 271, Kaunas LT-3009, Lithuania

Abstract

Vanadium pentoxide based xerogels, H2V12O31-y∙nH2O, have been extensively studied over past years because of their particular properties. These materials can be used as reversible cathodes in lithium batteries, electrochromic layers for display devices, host materials for the intercalation of guest species, humidity sensors, starting material for switching elements, and so on. These xerogels have a layered structure where V2O5 chains are bonded by interlayer water, and can intercalate guest ions and molecules.

Partial substitution of vanadium ions by a metal of higher valence (Mo, Cr) in hydrated vanadium oxides leads to a decrease of the electronic part of conductivity. The X-ray photoelectron spectroscopy (XPS) spectra of hydrated vanadium oxides
(VO)MoxV12-x×nH2O (X = 0, 1, 2, 3) has been studied to provide the vanadium ions reduction ratio RR = V4+/(V4++V5+) dependence on the molybdenum ions concentration and the thermal treatment. The analysis of vanadium and molybdenum XPS spectra of the thermally untreated samples demonstrate that either V 2p3/2 and Mo 3d5/2 lines shape is actually independent on the molybdenum concentration within 0 ≤ x ≤ 3 interval. It was shown, that RR » 0.18 is same that for the all tested samples, while molybdenum is in the main Mo6+ oxidation state. It indicates that charge transfer V4++Mo6+ ↔ V5++Mo5+ between V and Mo ions do not take place. The temperature desorption mass spectroscopy analysis shows that for (VO)V12×nH2O xerogel intensive desorption of oxygen from xerogels begins at Tk ≈ 460K. The significant, of about 0.13, increase of vanadium ions RR for the samples backed below and above Tk may be related with an appearance of additional O2- vacancies due preferential oxygen evaporation above Tk.

It was concluded that the appearance of V4+ ions in V2O5-based xerogels is mainly related with the stoichiometry of the samples, while higher valence admixture ions acts only as a diluting component.

 

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Presentation: Poster at E-MRS Fall Meeting 2007, Symposium J, by Sigitas Mickevicius
See On-line Journal of E-MRS Fall Meeting 2007

Submitted: 2007-05-11 09:50
Revised:   2009-06-07 00:44