Low-frequency superelasticity and nonlinear elastic behavior of SrTiO3 crystals

To clarify the inconsistencies in existing elastic constant data of SrTiO3 in the vicinity of the 105 K phase transition we have studied the temperatu re dependence of the Young's modulus of SrTiO3 crystals. Dynamic mechanical analysis at 10-140 K and 10-45 Hz has been used for the experiments. We fo und two remarkable features: a giant elastic softening (superelasticity) be low the cubic --> tetragonal phase transition, and elastic anomalies in the quantum paraelectric region between about 25 K and 45 K. The giant elastic softening is caused by domain-wall motion: it can he suppressed with uniax ial compression and does not occur in the [111] direction. Elastic anomalie s observed in the quantum paraelectric region display nonlinear elastic beh avior. We relate these nonlinear elastic anomalies with the appearance of p olarization clusters. Our data can be consistently described assuming a fre ezing of the dynamical polar clusters below 25 K.