Optical properties of Fe-doped BaTiO3 films deposited on quartz substrates by sol-gel method

The Sellmeier's single oscillator function, n2 = S+EcEd/(Ec2−E2), is related to the electronic structure of the films. Here S, Ec and Ed are the contribution from high-energy CP transitions, the oscillator energy and the dispersion energy respectively. The model was used to fit the refractive index n in the transparent region. As can be seen from the Figure, S value decreases with increasing Fe composition, indicating the contribution from high-frequency electronic transitions becomes less. Both Ec and Ed generally increase with the Fe concentration. The maximum electronic transition appears near the photon energy range of 2.56−3.29 eV from the fitted oscillator, smaller than the Eg and nearly agree with the k observed. It suggests that the optical dispersion in the transparent region is mainly due to the higher CP virtual transitions.134