Enhanced electrocaloric effect within a broad temperature range in lead-free polymer composite films by blending the rare-earth doped BaTiO₃ nanopowders

This paper investigates the electrocaloric effect (ECE) in polymer nanocomposite films containing ferroelectric poly (vinylidene fluoride-trifluoroethylene-chlorofluoroethylene) [P(VDF-TrFE-CFE)] terpolymer matrix and lead-free nanopowders. The nanopowders include pure BaTiO₃ and rare-earth substituted Ba_0.94R_0.04TiO₃, where R = La, Nd, Sm, prepared by a modified sol-hydrothermal method. The substitution influences the lattice parameters, but all samples exhibit a perovskite-type tetragonal phase. The dopant enhances the relaxation behavior of the matrix and decreases the current. Using the Maxwell equations, the ECE performance is systematically studied for all samples. As the rare-earth ionic radius decreases, the Curie temperature of the nanocomposite increases and the dielectric constant decreases. The isothermal entropy changes (ΔS), adiabatic temperature changes (ΔT), cooling energy densities (Q), and electrocaloric strengths versus temperature exhibit different dependences on electric field (E). The results demonstrate that rare-earth doping can effectively modify the ECE. Our composites achieve large EC strength values (|ΔT|/|ΔE|) of 7 to 21 μK m kV⁻¹ over a wide temperature range of 25 to 60 °C and electric field range of 750 to 1250 kV cm⁻¹ and provide typical examples of polymer ECE materials containing rare-earth doped nanopowders. Graphical abstract: The preparation of the polymer nanocomposites and the adiabatic temperature changes and the corresponding electrocaloric strengths of the samples. [Figure not available: see fulltext.]