The inevitable defect carriers in dielectric capacitors are generally considered to depress the polarization and breakdown strength, which decreases energy storage performances. Distinctive from the traditional aims of reducing defects as much as possible, this work designs (FeTi ′ – Vo ••)• and (FeTi ″ – Vo ••) defect dipoles by oxygen vacancy defect engineering in acceptor doped Sr2Bi4Ti(5–x)Fe x O18 layered perovskite films with n-type leakage conductance. It is shown that oxygen vacancies effectively capture electrons (carriers) in n-type dielectrics to enhance the breakdown strength. Meanwhile, defect dipoles provide a driving field for depolarization to engineer the generation energy of domains and the domain wall energy, which effectively lowers the residual polarization P r but not at the expense of the maximum polarization P max as relaxor ferroelectric regulations. Such defect engineering effectively breaks through the limitation, in which the energy storage density suffers from the trade-off relationship between polarization and breakdown strength. The Sr2Bi4Ti4.92Fe0.08O18 film with the proper oxygen vacancy content achieves a high energy density of 110.5 J/cm3 and efficiency of 70.0% at a high breakdown strength of 3915 kV/cm. This work explores an alternative way for breakthroughs possible in the intrinsic trade-off relationship to regulate dielectric energy storage by defect engineering.

We define AO12 and BO6 oxygen polyhedra in layered perovskite films as A-O* and B-O* polyhedral dipoles, respectively, which is responsible for the spontaneous polarization and the construction of domains....

We report a distinctive way for designing lead-free films with high energy storage performance. By inserting different single perovskite cells into Bi4Ti3O12, P–E hysteresis loops present larger maximum polarization, higher breakdown strength and smaller slim-shaped area. We prepared 0.15Bi7Fe3Ti3O21-0.5Bi4Sr3Ti6O21-0.35Bi4Ba3Ti6O21 solid solution ferroelectric films employing the sol-gel method, and obtained high energy storage density of 132.5 J/cm3 and efficiency of 78.6% while maintaining large maximum polarization of 112.3 μC/cm2 and a high breakdown electric field of 3700 kV/cm. Moreover, the energy storage density and efficiency exhibit stability over the temperature range from 20 °C to 125 °C, and anti-fatigue stability maintains up to 108 cycles. The films with a simple preparation method and high energy storage performance are likely to become candidates for high-performance energy storage materials.

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