Dresden 2014 – wissenschaftliches Programm
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DF: Fachverband Dielektrische Festkörper
DF 20: Nonlinear dielectics, phase transitions, relaxors
DF 20.4: Vortrag
Donnerstag, 3. April 2014, 11:30–11:50, GER 37
Study of field induced critical point in relaxor ferroelectric single crystal and ceramics — •Nikola Novak1,3, Raša Pirc1, and Zdravko Kutnjak1,2 — 1Jožef Stefan Institute, Jamova 39, 1001 Ljubljana, Slovenia — 2Jožef Stefan International Postgraduate School, Jamova 39, 1001 Ljubljana, Slovenia — 3Institute of Materials Science, 64287 Darmstadt, Germany
Relaxor ferroelectrics represent a class of disordered ferroelectrics, which are characterized by the absence of long range ferroelectric order in zero applied field at any temperature. The study of the third-order nonlinear dielectric permittivity some time ago predict a first-order phase transition into a ferroelectric state by cooling a relaxor in an electric field E larger than some threshold electric field Ec.
In order to investigate the field-induced phase transition in relaxor ferroelectric a high-resolution calorimetric and polarization measurements were utilized along the Ec(T) transition line. The behavior of the heat capacity as a function of the temperature and electric field as well as the vanishing of the latent heat gives a sharp defined critical point in [110] relaxor ferroelectric single crystal Pb(Mg1/3Nb2/3)O3 (PMN). On the other hand in 9/65/35 PLZT ceramic the heat capacity as a function of electric field shows a crossover from a discontinuous to continuous step, however, the sample temperature change as a consequence of released latent heat does not vanishes completely. The persisting of the sample temperature anomaly at high temperature can be attributed to two effects: i) the anisotropy of the critical point and ii) electrocaloric effect (ECE).