Isotopic Effect in Evolution of Structure and Optical Gap During Electrochromic Coloration of WO3·1/3(H2O) Films

Abstract

Evolution of the fundamental absorption edge and structure of WO3 · 1/3(H2O) films during electrochromic (EC) coloration with different cations has been studied in situ by optical and Fourier-transform Raman spectroscopy to clarify the role of inserted cations. With EC coloration, different high-energy shifts of the optical gap have been observed in the absorption spectra of the films coloured with H+ and D+ ions. The shift magnitude for coloration with H + ions is about twice that for coloration with D+ ions at the same electron density. Analysis of the shifts of the vibration bands during EC coloration with H+ and D+ ions has shown that along with a lattice polarization induced by the injected electrons forming the polarons, a strong lattice distortion produced by inserted ions occurs as well. The large isotopic effect shows that the electronic structure of WO-octahedra is very sensitive to ion-insertion, and the electron rearrangement depends not only on the charge and radius of the inserted ions but also on their mass.