Effect of Low Temperature Annealing on Microstructural and Optical Properties of $(BaTiO_3)_{0.84}(CeO_2)_{0.16}$ Thin Films

$(BaTiO_3)_{0.84}(CeO_2)_{0.16}$ thin films were prepared by electron beam evaporation method. X-ray diffraction and scanning electron microscopy revealed the amorphous structure for the as-prepared films. The thin films were annealed at temperatures: 200, 300, 400 and 500C for 1 h in air. Small and low intensity crystalline peaks were observed at annealing temperature of 200C for 1 h. The intensity and the number of the crystalline peaks were increased with increasing annealing temperature. Nanocrystals, of dimensions in the range 60-76 nm, were obtained when the annealing was performed at 500°C. The indexed diffraction pattern of the annealed thin film revealed a monoclinic structure. A two-layer model was used to describe the experimental ellipsometric data. The Bruggeman effective medium approximation was used to describe the surface roughness layer and the Cauchy dispersion relation was used to describe the main $(BaTiO_3)_{0.84}(CeO_2)_{0.16}$ layer. The optical constants of the thin films over 300-1100 nm spectral range were measured. The optical band gap showed gradual decrease with the annealing temperature. The accurate determination of the optical constants of the thin films is very useful and should be taken into consideration in the design of devices using optical thin films technology.