Optical phonons probe of the SrLaAlO4 crystal structure

We present a study of the vibrational properties of SrLaAlO4 based on Raman scattering and IR measurements of an oriented single crystal. All the four Raman and seven IR phonons allowed by symmetry for the tetragonal 14/mmm space group have been identified. The measured phonon frequencies in SrLaAlO4 are compared with those calculated on the basis of the shell model. Besides the Raman allowed phonon peaks, a number of additional Raman structures appear in the measured spectra. Some of them have been related to defects or second-order scattering processes. Three peaks with well defined symmetries appeared in forbidden scattering geometries. The symmetry of these peaks suggests short range ordering of Sr and La over lattice sites of the same symmetry.