Nonlinear elastic behaviour of SrTiO3 crystals in the quantum paraelectricregime

The ultra-low-frequency (Hz region) elastic behaviour of SrTiO3 has been ex amined over a wide temperature range including the cubic-tetragonal transit ion at T-c = 105 K and the quantum paraelectric region (T < 40 K) using a t hree-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 stre ss. In the quantum paraelectric regime we have detected nonlinear elastic a nomalies in the real and imaginary parts of the complex Young's modulus. Ou r data can be consistently described if we assume that ferroelectric order is induced by the applied strain gradient, which due to flexoelectric coupl ing is equivalent to a homogeneous electric field. Below 25 K the induced o rdered polarization clusters are frozen on the experimental timescale (11 H z).