Abnormal Elastic Changes for Cubic-Tetragonal Transition of Single-Crystal SrTiO_3

Strontium titanate (SrTiO_3) is a typical perovskite-type ceramic oxide and studying its high-pressure phases are critical to understand the ferroelastic phase transition. SrTiO_3 also can be used as an important analog of davemaoite (CaSiO_3) to understand the compositional and velocity structure of the Earth's interior. However, the high-pressure studies on the cubic-to-tetragonal phase transition pressure and elastic properties remain unclear for SrTiO_3. Here, we investigate the phase transition and elasticity of single-crystal SrTiO_3 by Raman and Brillouin scattering combined with diamond anvil cell. The acoustic velocities of single-crystal SrTiO_3 and the independent elastic constants of cubic and tetragonal SrTiO_3 are determined up to 27.5 GPa at room temperature. This study indicates that C_11, C_12, and C_44 exhibit abnormal changes at 10.3 GPa, which is related to the cubic-to-tetragonal phase transition. Interestingly, a significant softening on shear modulus and a large anisotropy of shear wave splitting (A_\mathrmS^\mathrmPO) jump are observed at 10.3 GPa. Using obtained elastic constants, the coefficients of the Landau potential are calculated to understand the phase transition between cubic and tetragonal. The calculated coefficients of the Landau potential are, \lambda_2 = 3.12\times 10^-2 GPa, \lambda_4 = -2.02 \times 10^-2 GPa, B^* = 1.34 \times 10^-4 GPa and B = 1.66\times 10^-4 GPa. The elastic results have profound implications in understanding the structure of the Earth's interior and indicate that the presence of tetragonal Ti-bearing CaSiO_3 helps to explain the large A_\mathrmS^\mathrmPO of the Earth's mid-mantle.