| Strontium titanate has been extensively studied for its phase transitions, critical phenomena and relaxation effects, which take place in this seemingly ordinary perovskite compound. The compound in its defect free state shows a dielectric constant that increases with decreasing temperature and appears to saturate below 3 K but displays no sign of a ferroelectric transition, regardless of its similarities to the ferroelectric BaTiO3. However, the introduction of a slight perturbation, such as strain, defect or electrical field to SrTiO3 will immediately induce ferroelectricity in the sample. The failure for SrTiO3 in its defect and strain free state to reach into a ferroelectric state has been attributed to the quantum fluctuation associated with the large zero-point motion of Ti atom inside the oxygen octahedron. The ground state of SrTiO3 is therefore known as the quantum paraelectric state. The detailed evolution of ferroelectricity from the quantum paraelectric state remains unknown.; Additionally, numerous anomalies have been detected in optical, acoustic and neutronscattering measurements. The origins of the anomalies are still unclear. Although some authors suggested that they were the result of “quantum coherent state”, others proposed that they might be due to extrinsic imperfections in the sample.; In order to maintain the sample integrity by eliminating the possible introduction of physical and chemical defects to the samples, we decided to apply hydrostatic pressures up to 16 kbar to a SrTiO3 single crystal and measured their dielectric properties down to 1.4 K. By analyzing the temperature dependence of the dielectric constant and dielectric loss, we have found: the antiferrodistortive transition temperature increased linearly with the pressure; hydrostatic pressure stabilized the ferroelectric phase with the extrapolated critical pressure at –0.25 kbar at temperature equals 0 K; hydrostatic pressure induced a crossover between a quantum fluctuation region to a classical region; two distinct relaxations with different pressure responses appeared at low temperatures.; The results are discussed and compared with the recently calculated phase diagram. While they are in qualitative agreement, deviations do exist, suggesting modifications in calculations are needed. The relaxation data are complicated and more studies are necessary. |
