Strain and temperature-dependent dielectric permittivity of cubic SrTiO3: Self-consistent phonon theory calculations

We examine the strain effect on the dielectric permittivity of cubic SrTiO₃ (STO) with Self-Consistent Phonon (SCP) theory calculations. Despite the soft mode frequency overestimation with this theory scheme and workflow, our calculations predict the correct tendency of TO1 with respect to temperature and strain. We found that a uniform tensile strain leads to softer TO1 modes. In addition, the TO1 frequency drops suddenly to zero at a specific temperature in the presence of a ferroelectric transition. The square linear relation between TO1 and temperature is used to estimate the Curie Temperature (T_C), and the STO dielectric permittivity calculated with the Lyddane-Sachs-Teller relation follows the Curie-Weiss (CW) law; which can also be used to determine another T_C value. Results from both approaches are in good agreement with each other and show that T_C increases significantly even when the applied tensile strain is only a few percent.