Enhanced electrocaloric effect in Al₂O₃/P (VDF-TrFE-CTFE) nanocomposite: direct measurement by infrared thermal imaging

Poly (vinylidene fluoride)- based polymers have a relatively large electrocaloric effect (ECE) but low thermal conductivity. In some studies, the ECE obtained from indirect measurement deviates substantially from direct measurement. In this work, the ECE was investigated in composites containing the ferroelectric poly (vinylidene fluoride-trifluoro ethylene-chlorotrifluoroethylene) [P(VDF-TrFE-CTFE)] terpolymer and Al2O3 fillers. The ECE of the composites was directly measured using an infrared thermograph and indirectly obtained utilizing the Maxwell relation. The temperature changes obtained by indirect and direct measurements agree reasonably well with each other. In direct measurement, we found the temperature increase is larger than the temperature decrease at a high field or in the composites with a high concentration of nanoparticles, which can be attributed to the Joule heating effect caused by increased conductivity and dielectric loss. In the extreme case, the Joule heating dominates the temperature change, and only the temperature increase can be observed. Moreover, the temperature change is increased by more than 38% in the composite with 1.5% Al2O3 fillers. One reason for the enhanced ECE is the increase of the polar phase in terpolymer after the addition of the nanoparticles. At the same time, the thermal conductivity of the composite film is also increased by 21% due to the high thermal conductivity of Al2O3.