Brillouin scattering study on ferroelectric single crystal Sr2Ta2O7

Acoustic properties of strontium tantalite (Sr2Ta2O7) single crystals with perovskite-slab structure were investigated by micro-Brillouin scattering. The two elastic stiffness constants c22 and c33 were determined in the temperature range between −140 °C and 300 °C. The elastic constant c22 shows marked continuous softening on approaching phase transition temperature To around 167 °C from both sides, indicating ferroelastic and nearly second-order nature of this phase transition. The values of c22 can be well reproduced by the Landau theory including bilinear coupling (linear in strain, quadratic in order parameter) between order parameter and the strain. Hypersonic attenuation increases markedly around To, which seems to reflect not only bilinear coupling between the order parameter and the strain in the ferroelastic phase, but also electrostrictive coupling in the paraelectric phase.