Abstract
Thin films of CeVO4 prepared via the sol-gel route, with a tetragonal (I41/amd) crystalline structure, show good ion-storage properties. The sol-gel route combined with the dip-coating deposition technique allowed thin solid films and powders with a specific Ce/V molar ratio (Ce/V=2:1, 1:1 (CeVO4), 1:2) to be made. The structure of films and powders prepared at 400°C, and at different times of heat-treatment, was determined using X-ray diffractometry (XRD). It is shown that films containing more ceria than vanadia (Ce/V>1) are nanocrystalline with a CeO2 grain size up to 100 Å, but a tetragonal CeVO4 (Wakefieldite) phase is formed when the Ce/V molar ratio is 1:1. By using cyclic voltammetry it was possible to observe the Ce4+/Ce3+ and V5+/V4+ redox changes occurring in the films, while in-situ UV-VIS spectroelectrochemical measurements confirmed the sole presence of V5+/V4+ redox changes in tetragonal CeVO4 films. The small (~0.1-0.5 cm2/C) coloration efficiency of CeVO4 films suggests their utilization as counter electrodes in electrochromic (EC) devices. Comparison of the IR transmission spectra of as-deposited CeVO4 with CeVO4 films charged to x≅0.9 revealed that besides A2u and Eu modes - attributed to the VO43- stretching vibrations predicted by factor group analysis, the Raman active Eg and B2g modes appear in IR spectra. This suggests that inserted Li+ ions occupy the accessible sites within the structure resulting in the loss of inversion symmetry and the consequent disappearance of the distinction between g and u modes. Charging to x≅2.3 causes instability of the film structure.
Original language | English |
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Pages (from-to) | 195-214 |
Number of pages | 20 |
Journal | Solid State Ionics |
Volume | 118 |
Issue number | 3-4 |
DOIs | |
State | Published - 2 Mar 1999 |
Keywords
- CeVO
- Electrochromism
- In-situ UV-VIS spectroelectrochemistry
- Infrared and Raman spectra
- Li insertion
- Sol-gel
- Thin films
- X-ray diffraction