Fig. 1. Core level XPS spectra for BST03. (a) Ba 3d, (b) Sr 3d, (c) Ti 2p, and (d) O 1s. The solid lines are the fitting results using the XPS peak processing method.

Fig. 2. (a) XRD patterns of the prepared Ba_1-xSr_xTiO₃ films with x ranging from 0.1 to 0.9; (b) variation between the lattice parameter c and the composition x; (c) schematic display of epitaxial relationship between the film and the substrate.

Fig. 3. Optical transmission spectra in the wavelength range of 300–800 nm for the samples; inset, simulated envelopes of the interference fringes for BST03.

Fig. 4. Calculated linear refractive indices for the samples as a function of wavelength. The inset shows the relationship between the linear refractive index and the composition x at a typical wavelength of 532 nm.

Fig. 5. (a) OA and (b) CA z-scan normalized transmittance for the samples. The solid curves are the theoretical fits to the data.

Fig. 6. The variation of n₂ and β with the concentration x in Ba_1-xSr_xTiO₃.

Fig. 7. Sketch of Ti-O plane of tetragonal-structured BST.

Fig. 8. Variation of the normalized transmission with the input intensity for BST03 at 532 nm. The solid line is the theoretical fitting.