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Abstract
The complex susceptibility of SrTi18O3 (STO18) has been measured at frequencies 10−3 < f < 105 Hz and temperatures 5 < T < 90 K with ac field amplitudes 10 < E0 < 300 V/m in order to inspect the phase transition and its quantum nature, and to study the dielectric dispersion and loss of the “unknown” dipolar defects involved in the dielectric spectra at low temperatures. The phase transition turns out to be of second order, but slightly smeared and to possess mean-field quantum behavior. The dipolar defects are proposed to be due to V0 centers coupled to adjacent Ti3+ ions (trapped small polarons). Owing to their random charge nature they are assumed to be responsible for the random field-controlled domain wall response. At frequencies above their dipolar relaxation step they act as strong pinning centers involving frozen dipolar fields, which completely suppress any domain wall response to low driving fields E0.