Phase transition and random-field induced domain wall response in quantum ferroelectrics SrTi¹⁸O₃: review and perspective

The oxygen isotope exchange of 16O by 18O in SrTiO3 causes a drastic change from paraelectric to ferroelectric, due to the suppression of quantum fluctuation. The phase transition and origin of the huge domain wall response were evaluated by dielectric, magnetic (NMR), and optical measurements (SHG, light scattering). The results obtained corroborate (1) smeared ferroelectric transition at Tc due to quenched random field, (2) a quite large dielectric contribution from domain walls, (3) incomplete softening of the transverse optic mode, and (4) a large contribution from the relaxational mode to the phase transition. Quantitative explanations, given to individual results, may give hints to grasp the mechanism for the evolution of ferroelectricity, in which quantum fluctuation and random fields are dominant perturbations. Finally, some of the news studies on the SrTiO3 were also introduced.