Infrared optical properties of PbTiO₃ ferroelectric thin films

Infrared optical properties of lead titanate (PbTiO₃) thin films grown on Pt/Ti/SiO₂/Si substrates are studied by infrared spectroscopic ellipsometry (IRSE) in the spectral range of 2.5-12.6 μm. The refractive index and extinction coefficient of PbTiO₃ thin films are determined by fitting the IRSE data using a derived classical dielectric function formula. The refractive index decreases; on the contrary, the extinction coefficient increases as the wavelength increases. The absorption coefficient is greater than 1000 cm^-1 for wavelengths over 11.7 μm, but very small and less than 100 cm^-1 for wavelengths under 4.8 μm. The effective static ionic charge has also been derived, which is smaller than it would be in a purely ionic material for PbTiO₃ thin films.