Enhanced electrocaloric effect for refrigeration in lead-free polymer composite films with an optimal filler loading

Abstract

The electrocaloric effect (ECE) has been investigated in composites containing a ferroelectric poly(vinylidene fluoride-trifluoroethylene-chlorofluoroethylene) [P(VDF-TrFE-CFE)] terpolymer matrix and lead-free BaTi0.89Sn0.11O3 (BTSn11) fillers prepared by the solution-processed method. Large electrocaloric (EC) effect values including an adiabatic temperature change of ΔT = 9.08 K and an isothermal entropy change of ΔS = 79.0 kJ m-3 K-1 have been achieved in the BTSn11/P(VDF-TrFE-CFE) composite with 7.5 vol. % filler under an electric field of 1000 kV cm-1 at room temperature. Compared to the neat terpolymer and BTSn11 ceramics, the ECE in the composite is enhanced by about 50% and 1400%, indicating the synergistic effect of the matrix and filler. The EC strength of the polymer composites as a function of temperature and filler loading is calculated and |ΔT/ΔE| = 0.009 K cm kV-1 with 7.5 vol. % fillers at 40 °C is obtained, which is higher than most values reported previously in the polymer composites. Finite element simulation is used to explain the enhanced EC effect and mechanisms while composites with 7.5 vol. % BTSn11 display the best ECE performance from a filler content of 2.5 vol. % to 10.0 vol. %, which has not been clearly interpreted before.