The ion-beam-sputtering method was used to deposit mixed films on silica substrates. The concentration ranged from 0 to 17%, and the refractive index ranged from ∼2.7 to ∼2.3 in visible wavelength. All the structures of the as-deposited films were amorphous. The refractive index and the extinction coefficient decreased with increased concentration. High temperature annealing reduced the optical absorption for all films. There was a phase transition from amorphous to polycrystalline anatase at high temperature. Surface roughness, and thus optical scattering, increased drastically with the appearance of the phase transition. The phase transition temperature was higher for films with higher concentration. The ion-beam-sputtered mixed film could sustain higher temperature annealing, resulting in lower extinction coefficient, than that of the ion-beam-sputtered pure film. The phase diagram of the mixed film system was given.
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