Ex situ and In situ Infrared Spectroelectrochemical Investigations of V 2 O 5 Crystalline Films

Vanadium oxide films were prepared by dip‐coating from V‐oxoisoproxide sols and heating at 300°C for 1 h. Transmission electron microscopy combined with electron and X‐ray diffraction revealed that the films consist of disordered grains with an orthorombic structure . Electromotor force (emf), cyclic voltammetric (CV), and chronocoulometric measurements, combined with in situ ultraviolet‐visible (UV‐vis) spectroelectrochemical measurements, revealed similar electrochromic and electrochemical properties with other sputtered and sol‐gel derived films. IR absorbance and reflection‐absorption spectra, performed at near‐grazing incidence angle (NGIA) conditions (80°, P‐polarized), allowed us to compare the observed transverse optical (TO) and longitudinal optical (LO) frequencies obtained from the dispersion analyses of crystalline reflection IR spectra. TO and LO spectra of charged films show that interactions modify the terminal (vanadyl), bridging , and edge‐sharing stretching frequencies, suggesting that these interactions take place between the oxygens bordering the cavities in which ions are accomodated during charging. The red‐frequency shift of the stretching and disappearance of the bridging stretching mode can be used as a diagnostic tool to differentiate between films cycled in the safe and unsafe potential regions. A polaron absorption was observed above in the ex situ TO and in situ NGIA reflection‐absorption (LO) spectra of films charged in the safe potential region.