The electrocaloric effect (ECE) is the adiabatic temperature change or isothermal entropy change caused by the polarization change of a dielectric material when subjected to a change of external electric field. The electrostrictive effect is a form of elastic deformation of a dielectric induced by an electric field, associated with those components of strain which are independent of reversal field direction. It was found that both the ECE, e.g., adiabatic temperature change, and the electrostrictive strain in poly(vinylidene fluoride–trifluoroethylene–chlorofluoroethylene) (P(VDF–TrFE–CFE)) terpolymers are proportional to the square of the electric field. The adiabatic temperature change ΔT of ECE versus electric field can be illustrated using a modified Belov–Goryaga equation. ΔT is proportional to E2 when E is small. For electrostrictive effect, the rigid-ion model assumes that the anharmonic movement of the ions leads to the quadratic strain–electric field relation. The quotient of electrostrictive coefficient Q over the phenomenological coefficient β is empirically a constant, indicating that the larger the electrostrictive coefficient, the larger the ECE, which opens a new way to find out new electrocaloric materials.
Phonon Renormalization Induced by Electric Field in Ferroelectric Poly(Vinylidene Fluoride–Trifluoroethylene) Nanofibers
