Giant negative electrocaloric effect measured by indirect method in X-ray irradiated P(VDF-TrFE) films
Bo Li, Bin Yang, Hong Zhang, Jiajia Zhang, Qianjin Wang, Weishu Liu
Abstract
Flexible solid-state cooling devices with high efficiency are attracted to ferroelectric polymers with excellent negative electrocaloric (EC) effects. It is challenging to obtain a large negative EC effect in ferroelectric polymers due to the lack of tunable techniques. A giant negative EC response was obtained in the poly(vinylidene fluoride-trifluoroethylene) copolymers (P(VDF-TrFE), 70/30 mol ratios) irradiated with high-energy X-rays. The irradiated P(VDF-TrFE) films showed an adiabatic temperature change of −13.5 K at 40 MV/m under a dose of 5 Mrad obtained by the indirect method. This significant negative EC effect is attributed to the enhancement of crystalline due to the entry of polymer molecules into the amorphous to crystalline structure and the reduction of heat capacity due to the increase of crosslinking. In addition, X-rays irradiation improves the dielectric coefficient from 15 to 22. This research indicates that irradiation can modify the negative EC properties of ferroelectric polymers for solid-state cooling.