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Preparation and characterization of nanocrystalline V2O5 and mixed V/Ce oxide

Vanadium oxide V2O5 and mixed V2O5 with cerium oxides as a thin films at 78, 55, 38 and 32 atomic % of V were prepared via inorganic sol-gel process which is well known synthetic route. Thin films were obtained on glass substrate covered with SnO2: F by dip coated method. Our films were prepared for counter electrode in electrochromic devices. Improved electrochemical properties and cycling behavior of vanadium oxide films we obtained after the addition of CeO2. All films were investigated by cyclic voltammetry (CV), IR and Raman spectroscopy, atomic force microscopy (AFM), transmission electron microscopy (TEM), grazing-incidence X-ray reflectivity (GIXR), grazing-incidence small-angle X-ray scattering (GISAXS). The addition of cerium improved very much the electrochemical stability of vanadium oxide. The best intercalation properties and cycling durability were obtained for films prepared at 55, and 38 at % of V. The amorphous grains in the range 50-100 nm were observed on the film surface at 55 at % with AFM before and after cycling. The surface roughness decreased after cycling. At surface of films prepared at 38 at % of V show no grain structure. After the cycling increase the surface roughness and grain structure with typical grain size of 100nm was observed. Films were characterized with TEM to obtain the cross section of films. In films prepared from pure V oxide, the particle size about 5 nm was observed and the crystalline structure of V2O5 was detected. The simulation of crystalline structure gave even smaller crystallite (1 nm in size) and confirms orthorhombic structure of V2O5 with space group Pmn21. Samples prepared at 55 and 38 at % of V also prove the formation of V2O5 (orthorhombic structure with space group Pmn21) with particle size between 1-2 nm. No formation of crystalline CeVO4 or CeO2 was obtained. With IR and Raman spectroscopy the formation of VO43- tetrahedral species was confirmed in both samples. The characteristic band layered structure in all V/Ce oxides was revealed by (GIXR) method. The average grain radius <R>, obtained by (GISAXS) was correlated with layers thickness.

Nanocrystalline oxide films; GiISAXS; GIXR; TEM

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