Enhanced electrocaloric strength of P(VDF-TrFE-CFE) induced by edge-on lamellae

Abstract

For the past decade, a novel cooling technique based on electrocaloric (EC) materials has been intensively investigated as an environmentally friendly and highly efficient alternative to the conventional vapor-compression refrigeration. Among all the EC materials, relaxor terpolymer P(VDF-TrFE-CFE) has been demonstrated as a promising candidate owing to its large EC effect and superior thermal stability. However, for the terpolymer, the EC strength (represented by EC temperature change under unit electric field (ΔT/E)) is still far from being satisfactory, which limits the mass application of terpolymer as a viable cooling medium in civil applications. Here, an effective method is employed to induce edge-on lamellae into the terpolymer to enhance the EC strength. Owing to the dipolar moments in the edge-on lamellae, which could be rotated more easily in the out-of-plane direction by the electric field, the treated terpolymer with edge-on lamellae exhibits a much enhanced EC strength of 0.13 K m⁻¹ MV⁻¹. Further exploration also shows a significantly decreased coercive field in the treated terpolymer due to the induced edge-on lamellae, and hence larger dipolar-entropy change could be generated at a modest electric field. The results indicate that a relaxor-like β-phase may also contribute to the enhanced polarizability. More importantly, the terpolymer with edge-on lamellae exhibits high thermal stability within a broad temperature range near room temperature. This work emphasizes the critical role of crystal structure on the macroscopic properties of electrocaloric polymers.