Lattice dynamical investigation of the Raman and infrared wave numbers of Ruddlesden-Popper compound Sr3Ti2O7

The Raman and infrared vibrational modes have been investigated by using normal coordinate analysis for the tetragonal Sr3Ti2O7 compound having phase I4/mmm and symmetry D-4h(17). This is the second member of the Ruddlesden-Popper series Srn+1TinO3n+1 with n = 2. With ten short-range stretching and bending force constants, the calculation of the zone-centre vibrational modes has been done. All of the vibrational modes of the Sr3Ti2O7 compound have not been observed experimentally, and the existing vibrational modes have only been partially assigned. The Wilson's GF-Matrix Method has been used for the first time to obtain the appropriate theoretical assignments for the Raman and infrared vibrational modes for the Sr3Ti2O7 compound. The calculated vibrational modes are consistent with the available observed experimental data. For each normal mode of the Ruddlesden-Popper phase Sr3Ti2O7, the analysis of potential energy distribution has been done for the significant impact of stretching and bending force constants towards different vibrational modes.