Ultrasonic and Brillouin scattering measurements under pressure near the structural phase transition of strontium titanate

The elastic properties under pressure of crystals of perovskite structure are interesting for the geophysics, the solid-state physics and the chemistry. Our interest focuses on strontium titanate (SrTiO₃). This compound is a perovskite crystal, which is well known at low temperature but not under pressure. A cubic-tetragonal phase transition occurs at 105 K and ambient pressure. In the current study, the elastic properties under pressure of SrTiO₃ are determined using three different techniques: a low pressure ultrasonic technique up to 0.3 GPa (US LP), a new high pressure ultrasonic set-up, up to 7 GPa (US HP) and Brillouin scattering, up to 15 GPa (BS). Our values are in good agreement. We show that the pressure phase transition of SrTiO₃ is around 9 GPa at ambient temperature, in opposition with previous results. The elastic constants of strontium titanate show a non-linear behavior 5 GPa before the phase transition