Infrared spectroscopy of CaTiO3, SrTiO3, BaTiO3, Ba0.5Sr0.5TiO3 thin films, and (BaTiO3)5/(SrTiO3)5 superlattice grown on SrRuO3/SrTiO3(001) substrates

We investigated infrared-active phonons of CaTiO3, SrTiO3, BaTiO3, and Ba0.5Sr0.5TiO3 thin films, and a (BaTiO3)5/(SrTiO3)5 artificial superlattice by a Fourier transform infrared spectrometer with a grazing angle (48°) incident reflectance method. The longitudinal phonon energies of the thin films were different from those of the bulk material due to the lattice strain of the substrate. The Ba0.5Sr0.5TiO3 thin film and (BaTiO3)5/(SrTiO3)5 superlattice showed different phonon modes due to structural discrepancies, even though their chemical compositions are similar. The Ba0.5Sr0.5TiO3 thin film showed a single phonon energy lying between the phonon energies of BaTiO3 and SrTiO3 thin films, while the (BaTiO3)5/(SrTiO3)5 superlattice well preserved the characteristic phonon modes of BaTiO3 and SrTiO3 thin films.