Ref HAL: hal-03087910_v1
DOI: 10.1021/acs.jpcc.0c08237
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Résumé:

We report a combined experimental and theoretical lattice dynamics study of the Ruddlesden–Popper layered compound Sr₂TiO₄. From inelastic neutron scattering experiments, we derive the generalized phonon density of states of Sr₂TiO₄. 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 Sr₂TiO₄.