Abstract
Exceptionally high electro-caloric effects (ECEs) are observed in nanocomposites consisting of poly(vinylidene fluoride-co-trifluoroethylene) (VDF–co–TrFE) copolymer and barium titanate (BT) nanoparticles and nanowires. The poly(VDF–co–TrFE) matrix nanocomposites containing 5% volume fraction of BT nanowires are found to exhibit a negative ECE temperature change as large as 12 °C or a refrigeration effect of 8.3 J/g, which is much larger than those reported to date. The mechanisms of negative ECE and the enhanced negative ECE in the nanocomposites consisting of poly(VDF–co–TrFE) and BT nanowires are explained by the Kauzmann theory on glassy polar states and the interaction between BT nanofillers and the copolymer matrix. The effects of geometries of BT nanofillers on the negative ECEs are elucidated by P-E loop measurements, and dielectric and dynamical mechanical analyses. The nanocomposites, with their enhanced negative ECE tuned by the geometries of BT nanofillers, provide us with promising ECE refrigerants for practical application to small-sized and environmentally-friendly ECE coolers in the heat management of electronic devices.
Highlights
The electro-caloric effect (ECE) of ferroelectrics has been studied for decades since it was first discovered by Kobeko and Kurchatov in 1930 [1]
We report the negative ECE in ferroelectric copolymer-ceramic nanocomposite with the absolute value of ECE temperature change larger than 12 ◦ C, which is much larger than those reported to date
The effects of barium titanate (BT) nanofillers on the nanocomposites are investigated by dielectric and mechanical relaxation analyses
Summary
The electro-caloric effect (ECE) of ferroelectrics has been studied for decades since it was first discovered by Kobeko and Kurchatov in 1930 [1]. During the adiabatic polarization process, the dipoles in a ferroelectric material are arranged along an applied electric field and tend to be ordered. The entropy of the ferroelectric material decreases, and heat is produced and the temperature increases under the adiabatic condition. With the removal of the electric field, the dipoles become relatively disordered, resulting in an increase of entropy of the materials [2]. Giant ECEs have been found in ferroelectric polymers, ceramics and polymer-ceramic composites, much effort is still devoted to developing those novel electronic materials which could possess large ECE entropy change [3,4,5,6,7,8,9]. Some ferroelectric materials exhibit abnormal ECE which is in contrast to those aforementioned, suggesting that cooling occurs in the ECE materials with the application of an electric field and heating occurs in the materials with its removal. It has been found that the negative ECE temperature changes could be as high as ~6 ◦ C in (Pb0.97 La0.02 )(Zr0.95 Ti0.05 )O3 thin films and ~1 ◦ C in PbZrO3
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