Large electrocaloric refrigeration performance in ferroelectric polymer nanocomposite with complementary nano-structural fillers

Abstract

Electrocaloric (EC) refrigeration in nanocomposites provides sustainable heating and cooling through its excellent entropy change when applied or withdraw an electric field. Nonetheless, it's difficult to achieve a large EC performance under low electric fields since ferroelectrics have relatively low thermal conductivity and small diabatic temperature change. In this work, we design an EC nanocomposite by incorporating 12 %[0.68(BaZr_0.2Ti_0.8O₃)-0.32(Ba_0.7Ca_0.3TiO₃)] (BCZT) nanoparticles with significant ferroelectric properties and 7 %Boron Nitride nanosheets (BNNSs) with notable electrical insulation and ultra-high thermal conductivity into relaxor ferroelectric terpolymer P(VDF-TrFE-CFE), aiming to improve ECE performance and increase cooling power density of the nanocomposite. We attain an adiabatic temperature change (ΔT) of 8.85K, isothermal entropy change (ΔS) of 30.10J·kg⁻¹·K⁻¹ and isothermal cooling energy density (Q) of up to 5.10 × 10⁷ J·m⁻³ under a low electric field of 80 MV/m by direct method, which is an order of magnitude larger than those of other EC materials reported so far. The introduced interfacial coupling effect between ceramic and terpolymer plays a very important role to ECE, which modulates their polarization, microscale electric-dipoles changes, and energy conversion behavior, simultaneously improves the cooling power density of nanocomposite. Furthermore, the heat transfer performance of nanocomposite is simulated using Finite-element method (FEM) to investigate their heat transfer properties based on the solid-state heat transfer theory. The phase-field simulation has demonstrated the nanocomposite still possesses impressive ferroelectric properties under the influence of elastic compressive strain based on time-dependent Landau-Ginzburg-Devonshire (TLGD) theory. This research is of significant importance for achieving precise thermal management of the next-generation microelectronic devices.