Naslov
Preparation and Characterization of Nanocrystalline V/Ce Oxides

Autori
Crnjak Orel, Zorica ; Turković, Aleksandra ; Ivanda, Mile

Vrsta, podvrsta i kategorija rada
Sažeci sa skupova, sažetak, znanstveni

Izvornik
NANO 2004, 7th International Conference on Nanostructured Materials / Feist, Barbara ; Sporleder, Sabine - Frankfurt : Druckhaus K. Schmitt Wwe., 2004, 177-177

Skup
7th International Conference on Nanostructured Materials

Mjesto i datum
Wiesbaden, Njemačka, 20.06.2004. - 24.06.2004

Vrsta sudjelovanja
Poster

Vrsta recenzije
Međunarodna recenzija

Ključne riječi
V/Ce oxides; Raman; GISAXS

Sažetak
Vanadium oxide and mixed vanadium cerium (V/Ce) oxides thin films at 71, 55, 38 and 32 atomic % of V were prepared via inorganic sol-gel process. It is well known synthetic route for preparation of various oxide materials. In aqueous solution it starts with hydrolysis of inorganic precursors, followed by condensations, gelations, aging, drying and densification. All films were prepared on glass substrate covered with SnO2:F. Different materials have been prepared in this way with potential application in optical electronics, as protective films or as catalysts. Our films were prepared for counter electrode in electrochromic devices. The counter electrode provides electrochemical balance of the charge transferred during the oxidation and reduction reactions performed on primary electrochromic element. It must be transparent under a charge insertion for practical uses. It is well known that V2O5 is reversible, fast, but when the voltage was swept in the wider range disordered materials was obtained with continuous decrease of intercalation/deintercalation properties. Improved electrochemical properties and cycling behavior of vanadium oxide films we obtained after the addition of CeO2. The addition of Ce precursors influence on their electrochemical, optical and structural properties. All films were investigated by grazing-incidence X-ray reflectivity (GIXR), grazing-incidence small-angle X-ray scattering (GISAXS), cyclic voltammeter (CV), IR spectroscopy, UV-VIS technique, atomic force microscopy (AFM), transmission electron microscopy (TEM), Raman spectroscopy. The addition of cerium improved the stability of vanadium oxide with the ion-charge capacity (up to 30 mC cm-2). The intercalation of Li+ ions in V/Ce films was followed by FT-IR spectroscopy in combinations with CV measurements at wide potential range. The transmittance did not change significantly after cycling. 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 between 50 and 100 nm were observed on the film surface at 55 at % with AFM. After cycling the same size of grains were still observed, only the surface roughness decreased. At surface of films prepared at 38 at % of V no grain structure was observed but after the cycling increase the surface roughness and grain structure with typical grain size of 100 nm was observed. Films were characterized with TEM to obtain the cross section of films. Nice visible columnar grains of SnO2:F with 250 nm in diameter were detected. In pure V oxide the crystalline structure of V2O5 was confirmed without any preferential orientation. TEM of films prepared at 38 at % of V revealed formation of microcrystalite. That was identified as fluorite structure of CeO2 and was identified using microdifraction technique. Layered structure in all V/Ce oxides was revealed by grazing-incidence X-ray reflectivity (GIXR) method. The average grain radius <R>, obtained by grazing-incidence small-angle X-ray scattering (GISAXS) was correlated with layers thickness. Variation of film resistivity obtained by impedance/admittance spectroscopy is related to variation of porosity obtained by GISAXS. The structure of V/Ce mixed oxides is studied using infrared and Raman spectroscopies and the results are compared with X-ray spectroscopy data. Illustration is showing three-dimensional plot of GISAXS for V/Ce oxide at 38 at. % of V. Circles (m) are denoting reflectivity peaks for GIXR (grazing-incidence x-ray reflectivity) analyse, which reveals layers thickness.

Izvorni jezik
Engleski

Znanstvena područja
Fizika

POVEZANOST RADA