Interaction between quantum paraelectricity and ferroelasticity in SrTiO3

The dielectric susceptibility of SrTiO3 is measured as a function of temperature between room temperature and 32 K. These data show an anomaly at approximately 105 K, which is associated with the cubic-tetragonal ferroelastic phase transition. The form of this anomaly is shown to be consistent with biquadratic coupling between the ferroelectric and ferroelastic modes. The quantum paraelectric state of SrTiO3 is studied in the framework of a quantum mechanical Landau potential. The saturation temperature is determined from published measurements of the dielectric susceptibility at very low temperatures. When the coupling to the ferroelastic mode is accounted for, the saturation temperature obtained from these measurements (theta s = 20(1) K) is the same as that seen in phase diagrams for the ferroelectric transition, such as T-C versus chemical dopant or O isotope content.