Stability and Lattice Dynamics of Ruddlesden–Popper Tetragonal Sr 2 TiO 4

International audience ; We report a combined experimental and theoretical lattice dynamics study of the Ruddlesden–Popper layered compound Sr 2 TiO 4 . From inelastic neutron scattering experiments, we derive the generalized phonon density of states of Sr 2 TiO 4 . We also report its heat capacity, thermal expansion, and thermodynamic Grüneisen parameters using the calculated bulk modulus and find a large value of about 2. Using Raman scattering experiments under pressure, we discuss a potential structural distortion of the tetragonal structure above 11 GPa, which could be due to nonhydrostatic compression. The mode Grüneisen parameters of the four Raman-active modes are determined and shown to be in reasonable agreement with those obtained by density functional perturbation theory (DFPT) calculations. The temperature behavior of the Raman-active modes was studied, allowing us to determine the implicit volume and explicit anharmonic contributions. Above 400 K, the implicit volume contribution dominates the temperature-induced variation of the four Raman-active modes, whereas, below this temperature, the explicit anharmonic contribution is the dominant contributor to the highest energy mode. Our results underline the importance of anharmonicity in vibration-related properties of Sr 2 TiO 4 .