Fig. 1. Optical properties of the films: (a) transmittance; (b) refractive index n; (c) band gap of unannealed samples; (d) absorption.

Fig. 2. X-ray diffraction patterns of sample A (Ta₂O₅) and sample F (TiO₂) before and after annealing.

Fig. 3. Raman analysis of the samples before and after annealing. (a) Raman spectra. The dark curve represents the unannealed sample, while the light curve corresponds to the annealed sample. Vertical lines indicate the diffraction peaks position of TiO₂ anatase (gray lines) and rutile (black lines) phases. (b) First derivative of the normalized Raman spectra in the 550–750 cm^–1 region. (c) The horizontal coordinates (Raman shift) and the absolute values of the vertical coordinates corresponding to the extremum points of the normalized Raman spectra slopes for samples A–E.

Fig. 4. Typical XPS spectra of unannealed films: (a) Ta 4f; (b) O 1s (O_I refers to lattice oxygen, O_II corresponds to hydroxyl groups and O_III represents surface-adsorbed oxygen); (c) Ti 2p.

Fig. 5. The ratio of O_measured (measured oxygen content) to O_calculated (calculated stoichiometric oxygen content) in the films.

Fig. 6. Pair distribution function of the simulated amorphous Ta₂O₅ model.

Fig. 7. Theoretically calculated density of states: (a) Ta₂O₅; (b) 1V_O+1Ti_Ta; (c) 1V_O+2Ti_Ta; (d) 1V_O+3Ti_Ta. V_O represents an oxygen vacancy, which involves the removal of an oxygen atom. Ti_Ta refers to the replacement of tantalum with titanium.

Fig. 8. Differential charge distribution around Ti atoms in the 1V_O+2Ti_Ta model. The gold sphere represents a tantalum atom, the blue sphere represents a titanium atom and the red sphere represents an oxygen atom. The blue electron cloud indicates a loss of electrons, while the yellow cloud represents a gain of electrons.

Fig. 9. Theoretically calculated extinction coefficient k.

Fig. 10. Measurement of transmittance spectrum of high-reflectivity film.