Nonlinear optical properties of Bi0.5Na0.5TiO3 thin films grown by PLD

The present work investigates the role of oxygen partial pressure (PO2) during the thin film growth in obtaining phase and controlling the crystallinity and optical responses in the thin films. Rietveld refinement of X-ray diffraction confirmed a rhombohedral structure of BNT as a major phase with secondary phase of Bi2Ti2O7 and Bi4Ti3O12. The diminutions of the secondary phase are observed with an increase in PO2, which signifies the crystal structure closely related to the partial oxygen pressure. The refractive index of films was found to be improved and optical bandgap energy was reduced with PO2 due to the increase in crystallinity as well as decrease in oxygen vacancies. Nonlinear optical properties show a strong PO2 dependency, self-focusing behaviour with a positive, large optical nonlinearity (n2 = 4.62 × 10−6 cm2/W) and strong absorbance (β = 0.755 cm/W) for the film deposited at 10 Pa, which makes a potential candidate for the nonlinear photonic device applications.