Search

The effect of electric field on the paraelectric-to-ferroelectric phase transition has been studied by quasi-isothermal calorimetric measurements on the classical ferroelectric BaTiO3 (BTO) single crystal oriented in the [001] direction. The isothermal response of BTO exhibits a hysteresis at the field induced phase transition, however on approaching the critical point the asymmetry of the transition vanishes. The experimentally determined E-T phase diagram also shows a weak effect of the applied electric field on transition temperature at lower fields, whereas at higher fields the effect of the field becomes stronger.

The electric field induced ferroelectric transition was studied by polarization and quasi-isothermal measurements in relaxor Pb(Mg1/3Nb2/3)O3 (PMN) single crystal oriented in [110] direction. The polarization hysteresis loops and isothermal response of PMN exhibit a hysteresis at glassy to ferroelectric transition. Hysteresis effects are much stronger at lower temperatures indicating that the slowing glassy dynamics is mainly responsible for the phase transition hysteresis, and that the nonlinear effects related to electric-field induced ferroelectric domain switching become important only at higher temperatures close to the critical point.

We investigate PMN(1-x)-PTx single crystal with the composition x = 0.26, near the cubic-tetragonal-rhombohedral (C-T-R) triple point. We show the dielectric spectroscopy and heat capacity results obtained in PMN0.74-PT0.26 as a function of the bias electric field for [100] crystal axis. Dielectric and heat capacity data show that the electric field induced monoclinic phase sequence appears between tetragonal and rhombohedral phases. The impact of the bias field on the monoclinic phase sequence is studied as well as the impact on the critical behavior of the piezoelectric coefficient near the liquid-vapor type critical point.

The dielectric response of canonical relaxor PMN single crystal oriented in [111] direction was investigated under the influence of various dc bias electric fields. The behavior of the Vogel-Fulcher temperature obtained from the characteristic relaxation times determined from the peaks of the imaginary component ϵ″(T) of the complex dielectric constant ϵ*(T) was studied as a function of the dc bias electric field. The observed results reveal nonmonotonous behavior of the Vogel-Fulcher temperature as a function of the strength of the dc bias electric field. We show that such a behavior can be well interpreted in terms of nonlinear dielectric susceptibility as a dominant factor in the dielectric dynamic of relaxors in dc bias electric fields.

Presented in this paper of this special issue of Ferroelectrics, dedicated to Prof. Wolfgang Kleemann, is our recent study of thermal response near the dipolar glass to ferroelectric (G-F) transition studied by a high resolution calorimetry in relaxor ferroelectric 9/65/35 PLZT ceramics. By theoretical investigations based on spherical random bond random field (SRBRF) model it is predicted that the discontinuous electrocaloric change (EC) of temperature should be observed at the G-F transition line in an electric field–temperature (E-T) phase diagram. Experimental results confirm existence of such discontinuous EC jump in temperature in the canonical relaxor system 9/65/35 PLZT ceramics, thus confirming the existence of the first order G-F transition line in the E-T phase diagram of the perovskite relaxor ferroelectrics.