Calorimetric and dielectric study of vinylidene fluoride-trifluoroethylene-based composite

The paraelectric to ferroelectric phase transition in 9.5/65/35 lead lanthanum zirconate titanate-poly(vinylidene fluoride-trifluoro ethylene) ceramics-copolymer composite denoted as PLZT0.24[P(VDF0.5/TrFE0.5)]0.76 has been studied by means of calorimetry and dielectric spectroscopy. Results were compared to those obtained in pure poly(vinylidene fluoride-trifluoro ethylene) [P(VDF0.5/TrFE0.5)] copolymer. Heat capacity measurements reveal that the weakly first order paraelectric to ferroelectric transition becomes broadened and the heat capacity anomaly is suppressed in the PLZT-P(VDF/TrFE) composite. The excess enthalpy slightly increases in the dc bias electric field as a consequence of the improved field-induced ferroelectric long range ordering. It is shown that the transition takes place approximately in the middle of the temperature range in which the dielectric constant exhibits a significant break. The dielectric constant anomaly in the PLZT-P(VDF/TrFE) composite is also slightly broadened, however its peak value is enhanced by about 40%. The enhancement of the dielectric constant could be reasonably explained within the simple Maxwell-Garnett effective-medium approach.