Thermal expansion anomalies in the pre-cubic-to-tetragonal phase-transition range and the quantum paraelectric regime of SrTiO3

High-resolution dilatometry measurements have been made for SrTiO3 along the tetragonal-phase a and c axes and the cubic-phase [100] direction, for which a moderate stress field has been used accordingly to align the domains of the low-temperature tetragonal phase or to force a single domain. Anisotropy in thermal expansion just above the cubic to tetragonal transformation in the cubic phase for the measurements along the a and c directions has been observed. No structural change or strain anomaly has been detected in the low-temperature quantum-paraelectric (QPE) regime (K. A. Muller, W. Berlinger and E. Tosatti, Z. Phys., B84 (1991) 277). However, the continuing expansion of the tetragonal c axis with decrease of temperature is arrested below 10 K, which can be related to the QPE state