Temperature-Dependent Far-Infrared Reflectance Of An Epitaxial (Batio3)(8)/(Srtio3)(4) Superlattice

Infrared reflectance spectra of the polar optic phonons in a [(BaTiO3)(8)/(SrTiO3)(4)](50) superlattice over the temperature range 8 to 650 K are reported. The spectra exhibit lattice vibration features typical of the perovskite constituents, BaTiO3 and SrTiO3. Using the effective medium approximation for multilayer systems and a fitting procedure, we were able to successfully simulate the infrared reflectivity of the superlattice structures and extract the parameters and dielectric functions of the phonons. When applied at varying temperatures, this approach provides the parameters of the zone-center polar phonons and their temperature dependence. Comparing these results with x-ray diffraction we identified some anomalies in phonon behavior related to the phase transitions that the superlattice undergoes.