Electrochromic and structural investigation of InVO4 and some other vanadia-based oxide films

We extended our previous studies of M-3+VO4 orthovanadate (M3 + = Ce, Fe) and M-2(3+) V4O13 (Fe2V4O13) films to include InVO4 films because their photopic transmittance T-vis(initial) is above 0.885. Structural studies (TEM and XRD) revealed that films prepared from In(NO3)(3)5H(2)O and V-oxoisopropoxide sols annealed at 500 degreesC consist of the mixed monoclinic (InVO4-I) and orthorhombic (InVO4-III) phases, while the addition of acetylacetone (acac) to the sol results in amorphisation. The charge capacity of InVO4/acac films is between - 30 and - 40 mC cm(-2) (single dipped films) and their electrochemical stability is more than 1000 cycles. In situ UV-visible spectroelectrochemical measurements show that charging to - 35 mC cm (-2) decreases the photopic transmittance from T-vis(initial) = 0.885 to T-vis(ins) = 0.722, which contrasts the higher optical passiveness of previously investigated CeVO4 films (T-vis(ins) = 0.90). The increase in the broad absorption below 600 cm (-1) in IR spectra of charged/discharged InVO4 films shows that films irreversibly uptake lithium ions. Charging up to - 20 mC cm(-2) does not affect the IR spectra, while charging up to - 40 mC cm-2 results in the transformation of the film structure, which becomes similar to that of the amorphous InVO4 films obtained at 300 degreesC and to certain transition vanadate glasses. IR spectra of other vanadia-based films, i.e. FeVO4, Fe2V4O13, CeVO4, and V2O5 films in different state of lithiation are discussed. (C) 2001 Elsevier Science Ltd. All rights reserved.