On the microstructure and optical properties of Ba0.5Sr0.5TiO3 films

Thin films of Ba1-xSrxTiO3 (x = 0.5) are prepared on the (1 (1) over bar 02) plane of sapphire substrates with the pulsed laser deposition technique. Crystallographic studies show that the films are polycrystalline with a strong reflection along the (111) plane. Scanning electron micrographs reveal smooth surfaces. The index of refraction and the absorption coefficient are determined at room temperature in the wavelength range 382-800nm from spectrophotometer measurements of the transmittance at normal incidence, using the method devised by Swanepoel. The average value of the refractive index is found to be 2.06 in the visible spectrum, whereas higher values near the UV are associated with the fundamental bandgap absorption. The dispersion of the refractive index is interpreted in terms of a single electronic oscillator at 7.16 eV. The direct bandgap energy is found to be 3.96 eV. (C) 1997 Elsevier Science S.A.