Infrared optical properties of Ba0.8Sr0.2TiO3 ferroelectric thin films

Infrared optical properties of barium strontium titanate Ba0.8Sr0.2TiO3 thi n films grown on Pt/Ti/SiO2/Si substrates are studied by infrared spectrosc opic ellipsometry (IRSE) in the spectral range of 2.5-12.6 mum. The refract ive index and extinction coefficient of Ba0.8Sr0.2TiO3 are determined by fi tting the IRSE data using a classical dielectric function formula. As the w avelength increases, the refractive index decreases, but on the contrary, t he extinction coefficient increases. The absorption coefficient is greater than 1000 cm(-1) for the wavelength over 12.1 mum, but very small and less than 100 cm(-1) under 5.3 mum. The effective static ionic charge has also b een derived, which is smaller than it would be in a purely ionic material f or Ba0.8Sr0.2TiO3 thin films. (C) 2000 American Institute of Physics. [S000 3-6951(00)03649-4].