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Optical absorption in oxygen-deficient and Li+-ion inserted titanium oxide films was studied in the framework of small-polaron hopping. Non-stoichiometric TiOy films with 1.68 ≤ y ≤ 2.00 were deposited by reactive DC magnetron sputtering and were subjected to electrochemical intercalation of Li+-ions and charge-balancing electrons to obtain LixTiOy films with 0.12 ≤ x ≤ 0.34. Dispersion analysis was applied to calculate the complex dielectric function ϵ(ħω)≡ϵ1(ħω)+iϵ2(ħω) from numerical inversion of optical transmittance and reflectance spectra; a superposition of Tauc-Lorentz and Lorentz oscillator models was used for this purpose. Data on ϵ2(ħω) were employed to calculate the optical conductivity and fit this property to a smallpolaron model for disordered systems with strong electron-phonon interaction and involving transitions near the Fermi level. The introduction of oxygen vacancies and/or Li+ insertion yielded band gap widening by ~0.20–0.35 eV, and both processes induced similar low-energy optical absorption. The small-polaron-based analysis indicated increases in the Fermi level by ~0.15–0.3 eV for sub-stoichiometric and/or Li+-inserted films. This suggests the existence of polaronic Ti3+ states in the lower part of the conduction band arising from transfer of electrons from oxygen vacancies and/or inserted Li+ species. The present article is a sequel to an earlier paper on oxygen-deficient and/or Li+-inserted amorphous WOy thin films and forms part of a comprehensive investigation of optical absorption in amorphous transition metal oxides with different valence states of the metallic ions. [ABSTRACT FROM AUTHOR]

Thin films of LixWO3-z with 0 ≤ x ≤ 0.27 and 0 ≤ z ≤ 0.27 were prepared by sputter deposition followed by electrochemical lithiation. Kramers-Kronig-consistent complex dielectric functions were obtained for these films by numerical inversion of experimental spectra of optical transmittance and reflectance by using a superposition of Tauc-Lorentz and Lorentz oscillator models. Low-energy optical absorption bands were induced by oxygen vacancies and/or by electrochemical intercalation of Li+ species together with charge compensating electrons. The experimental optical conductivity was fitted to a small-polaron model for disordered systems with strong electron-phonon interaction, taking into account transitions near the Fermi level. The optical absorption is due to small-polaron hopping and associated with the formation of W5+ states due to transfer of electrons from oxygen vacancies and/or insertion of Li+ species. The results also show increases in the Fermi level, caused by oxygen deficiency or Li+ insertion, which occur along with a band gap shift towards higher energies for the Li+ intercalated films. [ABSTRACT FROM AUTHOR]