Synthesis and properties of the mixed hydrated oxides V2-y W y O5 + δ·nH2O

Abstract

Compounds of the general formula V2 - y W y O 5 + δ < eqid3 > nH2O (0 < y ≤ 0.25) with the layered structure of polyvanadic acid V2O5 < eqid4 > nH2O (H2V12O31 - δ < eqid5 > nH2O) have been prepared from peroxide solutions using the sol-gel process. The samples contain up to 5-8 wt% vanadium (IV). The water content changes within the range of 0.7 ≤ n ≤ 1.5 in depending on tungsten concentration. The V2 - y W y O5 + δ < eqid6 > nH2O (y ≤ 0.125) form the thin films described an interlayer distance of 11.60 ± 0.05 Å. The thermal properties, IR, and X-ray photoelectron spectra of the compounds synthesized have been studied. The thermal stability of the phases increases with the rising of tungsten content. The dehydration finishes with the forming solid solution V 2-y W y O5 and WO3. The electrical conductivity of V2-y W y O5 + δ < eqid7 > nH2O (0 < y ≤ 0.25) powders was measured between 293 and 473 K at a relative humidity of 12%. The activation energy of conduction is independent upon the W content and equals 0.22-0.24 eV. Partial substitution of vanadium for tungsten was found to reduce the conductivity of the phases. The conductivity of the films increases with the increasing of relative air humidity and is governed by proton diffusion across the V-O-W layers. © 2005 Springer Science + Business Media, Inc.