Infrared and Raman study of amorphous V2O5

Amorphous V2O5 can be obtained by cooling from the melt. This amorphous oxide is very sensitive to water vapour and can even be dissolved in water to give a vanadium pentoxide gel. The hydration process has been followed by infrared and Raman spectroscopy between 20 and 4000 cm−1. Short-range order in the amorphous oxide appears to be almost the same as in orthorhombic V2O5. The amorphous phase could even be described as made of small crystallites about 100 A in diameter. The structure of amorphous V2O5 does not seem to be modified by water adsorption, at least during the first stages of the hydration process. However, a drastic modification occurs when enough water is added to give a gel. A general shift to lower frequencies is observed, indicating a weakening of the VO bonds, presumably associated with the formation of new VOH2 bonds. Two different water species have been identified, one of which seems to be almost free of hydrogen bonding. Short-range order in the gels seems to be quite well defined and the spectra could be interpreted either in terms of crystallites, as in amorphous V2O5, or in terms of molecular (or macromolecular) species containing V2O5, (H2O), groups.