Synergism of CoFe2O4 additives and P(VDF-TrFE) barriers in crystallization, polar phase, and electrocaloric effects of multilayer composite thin films

Abstract

In the last decade, refrigeration technology based on electrocaloric effect (ECE) has become a research hotspot in the ferroelectric field, profiting from being environmentally friendly and highly efficient. In this paper, we fabricated CoFe2O4/P(VDF-TrFE) multilayer composite films on an fluorine-doped tin oxide glass by integrating CoFe2O4 additives and P(VDF-TrFE) barriers to innovate the structures and ECE performances. As a result, the multilayer composite films showed comprehensive superiorities such as higher crystallization, smaller grain size, more polar phase, smaller coercive fields, and higher polarizations than the reference P(VDF-TrFE) films. The composite films have acceptably low leakage currents far below micrometers at a high electric field of 100 MV m−1. We measured a giant ECE temperature change of 25.9 K and an ECE strength of 0.37 K m MV−1 at a relatively small external field of 70 MV m−1 for ferroelectric polymers, extremely competitive over the reported. The Landau–Devonshire theory ascertained the reliability of the ECE performance by the indirect method and predicted a high ECE temperature change of 54 K under 140 MV m−1 of the multilayer composite films. The giant ECE CoFe2O4/P(VDF-TrFE) multilayer composite films are prospective for solid-state refrigeration.