IN-SITU UV-VIS AND EX-SITU IR SPECTROELECTROCHEMICAL INVESTIGATIONS OF AMORPHOUS AND CRYSTALLINE ELECTROCHROMIC NB2O5 FILMS IN CHARGED DISCHARGED STATES/

Niobium oxide (Nb2O5) films and powders have been obtained via the sol -gel route from an NbCl5 precursor. XRD spectra revealed that films wi th pseudohexagonal (TT-phase) and orthorhombic (T-phase) structure wer e formed at 500 degrees C and 800 degrees C, respectively, while at 30 0 degrees C films were amorphous. Infrared (IR) and Raman spectra of p owders and films of Nb2O5 in different polymorphic forms were detected , and vibrational band assignments were made. Electrochromic propertie s of amorphous films and films with the TT-phase were established from in situ ultraviolet visible (W-Vis) spectroelectrochemical measuremen ts and correlated with ex situ IR transmission spectra of charged film s. Ex situ IR spectra revealed that charging of amorphous films is acc ompanied by variations of the Nb-O stretching mode intensity, while, f or films with the TT- and T-phase, splitting of the Nb-3-O stretching modes and the appearance of polaron absorption were noted with Li+ ion insertion. Ex situ X-ray diffraction (XRD) spectra of charged films w ith the TT-phase showed changes of the unit cell dimensions with charg ing. The influence of the polaron absorption on the ex situ near-grazi ng incidence angle (NGIA) IR reflection-absorption spectra of charged/ discharged films is discussed in detail.