Study of amorphous and crystalline phases of sodium bismuth titanate thin films by optical and Raman spectroscopy

Amorphous and crystalline Na 0.5 Bi 0.5 TiO 3 (NBT) thin films were deposited at different substrate temperatures on fused silica by plused laser deposition method. The phase and microstructure of the deposited films were investigated by XRD and FE-SEM respectively. The noticeable difference is observed in the Raman and optical spectra of amorphous and crystalline films. To grasp further insight, the dispersion data of the refractive index is fitted with the single oscillator model. The oscillator strength and oscillator energy are computed. The refractive index of NBT thin films decrease with increase in wavelength and approach a constant value in long wavelength limit while extinction coefficient increase with increase in wavelength. In Raman spectra of amorphous materials, many Raman peaks coalesce and form very broad spectral bands, whereas the polycrystalline material shows distinct band.