In situ UV-Vis and ex situ IR spectroelectrochemical investigations of amorphous and crystalline electrochromic Nb2O5 films in charged/discharged states |
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Authors: | Boris Orel Marjeta Ma?ek Jo?e Grdadolnik Anton Meden |
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Institution: | (1) National Institute of Chemistry, Hajdrihova 19, 1001 Ljubljana, Slovenia Tel.: +386-61-1760-276; Fax: +386-61-1259-244; e-mail: Boris.Orel@ki.si,;(2) Faculty of Chemistry and Chemical Technology, University of Ljubljana, Aškerčeva 5, 1001 Ljubljana, Slovenia, |
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Abstract: | Niobium oxide (Nb2O5) films and powders have been obtained via the sol-gel route from an NbCl5 precursor. XRD spectra revealed that films with pseudohexagonal (TT-phase) and orthorhombic (T-phase) structure were formed
at 500 °C and 800 °C, respectively, while at 300 °C films were amorphous. Infrared (IR) and Raman spectra of powders and
films of Nb2O5 in different polymorphic forms were detected, and vibrational band assignments were made. Electrochromic properties of amorphous
films and films with the TT-phase were established from in situ ultraviolet visible (UV-Vis) spectroelectrochemical measurements
and correlated with ex situ IR transmission spectra of charged films. Ex situ IR spectra revealed that charging of amorphous
films is accompanied by variations of the Nb-O stretching mode intensity, while, for films with the TT- and T-phase, splitting
of the Nb3-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 with the TT-phase showed changes of the unit cell
dimensions with charging. The influence of the polaron absorption on the ex situ near-grazing incidence angle (NGIA) IR reflection-absorption
spectra of charged/discharged films is discussed in detail.
Received: 21 August 1997 / Accepted: 9 October 1997 |
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Keywords: | Niobium oxide Infrared spectroscopy Films Electrochromism |
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