Thickness-dependent microwave dielectric and nonlinear optical properties of Bi0.5Na0.5TiO3 thin films

Lead-free Bi0.5Na0.5TiO3 (BNT) films were grown on Pt(111)/Ti/SiO2/Si and quartz substrates for various thickness by using pulsed laser deposition technique. The impact of thickness on structural, microstructural, Raman-spectroscopy, microwave dielectric and nonlinear optical properties have been investigated in detail. X-ray diffraction pattern of BNT films deposited at 700 °C showed rhombohedral crystal symmetry with a small secondary phase of Bi4Ti3O12 and also revealed that the lattice parameters, lattice volume, strain and crystallite size were enhanced with film thickness. The film thickness, refractive index and optical bandgap have been determined by Swanepoel's envelope method and Tauc relation and are in the range of 208 nm–1300 nm, 3.79 eV–3.28 eV and 2.41–1.80, respectively. The third order nonlinear optical properties of films were estimated by Z-scan technique and the 208 nm film exhibited strong nonlinear refractive index (n2 = 4.62 × 10−6 cm2/W) and nonlinear absorption coefficient (β = 0.796 cm/W). The enhancement in microwave dielectric properties was observed with film thicknesses which were measured by using SPDR technique. The leakage current density exhibited the space charge limited current conduction behavior. The enhanced microwave dielectric and nonlinear optical properties of BNT films are promising for microwave tunable and nonlinear photonic device applications.