Phase transition and random-field induced domain wall response of SrTi18O3

The dielectric permittivity epsilon'-iepsilon" of (SrTiO3)-O-18 (STO18) is studied under a dc electric field E as a function of the temperature, T. In epsilon' vs. T, a double-peak is found when 0 < E < 30 KV/m. While the peak at high-T is attributed to the smeared ferroelectric phase transition, the low-T one is induced by domain wall motion. The transverse Ising model including an external homogeneous and quenched random-fields is successfully used to describe both the smeared phase transition and the domain wall response in the low-T domain state. The calculations are in good agreement with the experimental results.