Lead-free BaBi4-xPrxTi4O15 (BBPT) relaxor ferroelectric films were prepared by the sol−gel method. A giant recoverable energy storage density of 47.8 J/cm3 and a high efficiency of 66.45% are obtained in BaBi3.9Pr0.1Ti4O15 (BBPT10) films. Specifically, the energy utilization ratio reaches as high as 0.0373. After 1 × 109 cycles, both the energy storage density and the efficiency can still be perfectly maintained. Moreover, BBPT10 capacitors possess outstanding thermal stability of energy storage performance over a wide temperature range of −20 °C to 120 °C. The breakdown strength reaches 1285 kV/cm. Such superb energy storage performances are mainly attributable to strong relaxation behaviors of the layered perovskite structure derived from the lattice distortion and structural transformation. BBPT based films provide a exploring area of lead-free ferroelectric materials widely applicable in energy storage devices.

PNP-type heterostructured films of P-type Na0.5Bi3.25La1.25Ti4O15 and N-type BaBi3.4Pr0.6Ti4O15 layers with the same Aurivillius layered perovskite structure are designed to regulate the energy storage performances by depletion region engineering.

Giant negative and positive electrocaloric effects (ECEs) coexist in lead‐free Na0.5Bi4.5Ti4O15 (NBTO) ferroelectric films with layered perovskite structure over a broad temperature range, with ΔT peaks of −14.8 °C (at 273 K) in the negative electrocaloric (EC) region (273–328 K), of 3.45 °C (at 373 K) in the positive EC region (328–418 K) and of −6.76 °C (at 483 K) in another negative EC region (418–513 K), respectively, under the electric field of 900 kV cm−1. Such giant ECEs are attributed to both the high break‐down electric field and prominent ferroelectricity. And the coexistence originates in the competition of the dipole polarization between both Na0.5Bi0.5TiO3 (NBT) and Bi4Ti3O12 (BTO) cells of NBTO films over the whole temperature region. Furthermore, the outstanding anti‐fatigue features with temperature stability for NBTO films ensure the durability of EC refrigeration. This work will prompt a novel technology for next generation of environmental‐friendly solid‐state cooling devices.

BaLaxBi4−xTi4O15 relaxor ferroelectric films with multilayered perovskite structure were prepared by the sol-gel method. Structural tunability is realized by layer selection engineering for La doping, which consequently regulates the energy storage performances. As x ≤ 0.2, Bi3+ is substituted by La3+ at perovskite-like layers, which increases the disorder degree of A-site cations and depresses the defects, it results in a high energy storage density of 44.7 J/cm3 and an energy storage efficiency of 60.1% in BaLa0.2Bi3.8Ti4O15 films under an applied electric field of 1667 kV/cm. While continuing to increase x, La3+ tends to enter (Bi2O2)2+ high resistance layers, which decreases the insulating properties and results in the reduction of the energy storage density. Moreover, good fatigue resistance after 108 polar switching and excellent thermal stability from −30 to 150 °C for energy storage performances are obtained by layer selection for La doping. This layer selection engineering for rare-earth doping provides an approach to regulate the energy storage performances in multilayered perovskite relaxor ferroelectric films.

Lead-free magnetoelectric composite films combining Bi 4 Ti 3 O 12 and CoFe 2 O 4 were synthesized by chemical solution deposition on Pt (100)/Ti/SiO 2 /Si substrate. Morphological and electrical domain structure, ferroelectric, leakage, dielectric, piezoelectric, magnetic and magnetoelectric properties were investigated for Bi 4 Ti 3 O 12 /CoFe 2 O 4 composite films. Well-defined interfaces between Bi 4 Ti 3 O 12 and CoFe 2 O 4 film layers and electrical domain structure were observed. The composite films show the coexistence of ferroelectric and ferromagnetic orders at room temperature. Larger piezoelectric coefficient and magnetization are obtained for the composite films, which is contributed to the magnetoelectric effect since it originates from the interface coupling through mechanical strain transfer. This work presents a feasible way to modulate the magnetoelectric coupling in ferromagnetic/ferroelectric composite films for developing lead-free micro-electro-mechanical system and information storage devices.