Effect of crystallization on optical properties of sol-gel processed nano-sized strontium titanate (SrTiO

Strontium titanate (SrTiO3) or ST thin films have been prepared using strontium 2-ethylhexanoate [ Sr[ CH3(CH$_{2})_{3}$CH(C2H5)CO2] 2] and titanium(IV) isopropoxide Ti[ OCH(CH$_{3})_{2}$] 4 as precursors using a modified sol-gel processing technique. The precursor [ Sr[ CH3(CH$_{2})_{3}$CH(C2H5)CO2] 2] was synthesised in the laboratory. Transparent and crack-free films were fabricated on pre-cleaned quartz substrates by spin coating. The structural and optical properties of films annealed at different temperatures have been investigated. The as-fired film was found to be amorphous while crystalline, cubical phase structure film was obtained after annealing at 550 °C for one hour in air. The films are polycrystalline in structure with the lattice constants of a = 3.90 Å. The grain sizes of the films annealed at 450, 500 and 550 °C were found to be 26.4, 31.8 and 35.2 nm, respectively. The optical constants of the films (refractive index, extinction coefficient, optical conductivity, complex dielectric constant, and energy band gap) were determined from the transmittance spectra. The refractive indexes of the films were found to increase while the optical band gaps were found to decrease with annealing temperature. The optical dispersion data are also analysed in the light of single oscillator model and are discussed