Electrical field dependence of electrocaloric effect in relaxor ferroelectrics

Relaxor ferroelectrics demonstrate great potential in achieving large electrocaloric effect (ECE) which could be used as cooling devices in microelectronics industry as well as in daily life. The electrical field dependence of ECE, however, remains unclear, especially for relaxor ferroelectrics. The electrical field dependence of ECE can help to predict the ECE characteristics of cooling devices, and facilitate the design of highly efficient refrigerators. In this work, relaxor ferroelectric 0.71Pb(Mg1/3Nb2/3)O3–0.29PbTiO3 (PMN–PT) (011) single crystals, (PbLa)(ZrTi)O3 ceramic thin films, and poly(vinylidene fluoride–trifluoroethylene–chlorofluoroethylene) (P(VDF–TrFE–CFE))/poly(vinylidene fluoride–trifluoroethylene) (P(VDF–TrFE)) terpolymer/copolymer blends were used to investigate the electrical field dependence of ECE. Direct method was used to measure the ECE adiabatic temperature change as a function of electrical field. Results indicate that, the ECE temperature change tends to show quadratic relationship, i.e., ΔT–E2, at lower electrical fields. At higher fields, however, the temperature change has a tendency towards saturation in terms of the relationship, i.e., ΔT–E2/3. In the intermediate electrical fields, the temperature change shows a roughly linear relationship with electrical field. The above phenomena could be illustrated in the frame of approximately continuous phase transition derived Belov–Goryaga equation, which can be modified for ferroelectrics.