Multifunctional Flexible Ferroelectric Thin Films with Large Electrocaloric Effect and High Energy Storage Performance.

Flexible ferroelectric films with high polarization hold great promise for energy storage and electrocaloric (EC) refrigeration. Herein, we fabricate a lead-free Mn-modified 0.75 Bi(Mg 0.5 Ti 0.5 )O 3 -0.25 BaTiO 3 (BMT-BTO) thin film based on a flexible mica substrate. Excellent EC performance with maximum adiabatic temperature change (Δ T ∼23.5 K) and isothermal entropy change (Δ S ∼33.1 J K -1 kg -1 ) is achieved in the flexible BMT-BTO film, which is attributed to the local structural transition and lattice disorder near 90 °C. Meanwhile, a good energy storage density of ∼70.6 J cm -3 and a quite high efficiency of ∼82% are realized in the same ferroelectric film, accompanied by excellent stability of frequency and electric fatigue (500-10 kHz and 10 8 cycles). Furthermore, there is no apparent variation in performance under different bending strains. These prominent properties indicate that the multifunctional BMT-BTO ferroelectric film is a promising candidate for applications of flexible energy storage and EC refrigeration.