Determination of vanadium valence in hydrated compounds

Vladimir Bondarenka 1Sergej Grebinskij 1Sigitas Mickevicius 1Henrikas Tvardauskas 1Saulius Kaciulis 2

1. Semiconductor Physics Institute, A.Gostauto 11, Vilnius LT-2600, Lithuania
2. Istituto per lo Studio dei Materiali Nanostrutturati (ISMN-CNR), Monterotondo, Roma I-00016, Italy

Abstract

Physical properties of vanadium pentoxide based compounds are strongly affected by the presence of vanadium ions of reduced valence. Thus, the identification of V4+ ions in mixed valence compounds and the determination of the reduction ratio RR=V4+/(V5++V4+) is an actual task.
Quantitative information of the relative amount of element species may be obtained from XPS data. The knowledge of BE and FWHM for individual species is required for the accurate deconvolution of the experimental spectra. Unfortunately, the known values of BE and FWHM show large discrepancy and cannot be directly used in fitting procedure.
The aim of this work is to study the main XPS peak parameters (such as BE and FWHM) of the minor V4+ ions diluted in the host V2O5 matrix. For this purpose the XPS spectra of the samples with different V4+ ions concentrations and the identical crystal structure were analyzed. In this case, the crystal field is the same for various valence ions, and only the vanadium ions charge affect on the chemical shift and FWHM.
Polyvanadium acid xerogel - H2V12O31.nH2O was used as a reference material. The spectra differentiation technique indicate that the replacing of (H2)2+ by a (VO)2+ cations allows to increase the RR of about 7%. Additional annealing of (VO)V12O31.nH2O xerogel increases the of reduced valence V4+ - ions concentration The spectra comparison technique was used to determine chemical shift and FWHM of V4+ cations in the vanadium pentoxide matrix. It was found that binding energy of V4+ ions shifts to the lover energy side of about 1.3 eV in respect to the main V5+ ions in the host matrix, while for pure main valence VO2 and V2O5 this difference is about 0.6 eV. FWHM in V2O5 based compound is actually the same for both minor V4+ and major V5+ ions in contrast to the main valence vanadium oxides.

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Presentation: poster at E-MRS Fall Meeting 2003, Symposium B, by Sigitas Mickevicius
See On-line Journal of E-MRS Fall Meeting 2003

Submitted: 2003-05-08 15:21
Revised:   2009-06-08 12:55
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