Optical properties of multilayer BaTiO$_{3}$/SiO$_{2}$ film structures formed by the sol–gel method

Multi-layer film structures BaTiO$_{3}$/SiO$_{2}$ with a thickness of $\sim$1 $\mu$m containing up to 14 pairs of layers were synthesized by the sol–gel method with sequential heat treatment. It is shown that the synthesized structures are X-ray amorphous. The formation of bands in the transmission and reflection spectra caused by interference effects is demonstrated. A more regular structure exhibits a photon band gap (opacity band) in the visible range with main minimum at 636 nm and corresponding maximum in the reflection spectra. Dispersion characteristics of barium titanate films with different concentrations of initial sols were studied and an increase in the refractive index with an increase in the concentration of sol was demonstrated. For a sol with a concentration of 60 mg/mL, the refractive index in the spectral range of 390–1600 nm is 1.88–1.81. The prospects of sol–gel technology for the formation of BaTiO$_{3}$/SiO$_{2}$ structures for nanophotonics and solar radiation converters are discussed.