Nonlinear elastic behaviour of SrTiO 3 crystals in the quantum paraelectric regime

The ultra-low-frequency (Hz region) elastic behaviour of SrTiO 3 has been examined over a wide temperature range including the cubic-tetragonal transition at T c = 105 K and the quantum paraelectric region ( T < 40 K) using a three-point–bending method. A giant elastic softening has been found in the tetragonal phase. It is explained by a model, which takes into account the motion of ferroelastic domain walls in response to the applied dynamic stress. In the quantum paraelectric regime we have detected nonlinear elastic anomalies in the real and imaginary parts of the complex Young's modulus. Our data can be consistently described if we assume that ferroelectric order is induced by the applied strain gradient, which due to flexoelectric coupling is equivalent to a homogeneous electric field. Below 25 K the induced ordered polarization clusters are frozen on the experimental timescale (11 Hz).