Structural, ultraviolet-shielding, dielectric and ferroelectric properties of Ba_1-xSr_xTiO₃ (x=0.35) thin films prepared by sol-gel method in presence of pyrrole

Barium-strontium titanate thin films were prepared by the sol-gel (SG) method. The Barium-strontium titanate sol was derived from organometallic compounds and modified by pyrrole. The films derived from pyrrole were uniform and crack free. The structural evolution of the film was investigated by X-ray diffraction (XRD). The thickness of the film increased by twofold (645 nm) when pyrrole concentration was increased from 0 to 1.5 molar ratio with respect to titanium. Barium-strontium titanate films showed excellent UV absorption and transparency in the visible region. The direct band gap of barium-strontium titanate films was determined from the curve of absorption coefficient (α) vs. hν and was found to be 3.9 eV. The refractive index of the 500-nm-thick annealed film was 2.5. The dielectric constant and dielectric loss values of modified films annealed at 700 °C were 680 and 0.05, respectively, measured at 1 MHz. The dielectric constant increases and dielectric loss decreases, with increasing pyrrole concentration. The dielectric properties were also investigated with annealing temperature of barium-strontium titanate films. The grain size of the films varied with annealing temperature. The remanent polarization (P_r) and coercive field (E_c) of films made from the sol-gel method with pyrrole, were found to have average value of ≈ 2.2 μC/cm² and ≈ 21 kV/cm, respectively.