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Ba-doped multiferroic BiFeO3thin films were successfully prepared on Pt/TiO2/SiO2/Si(1 0 0) substrates by pulsed laser deposition. X-ray diffraction showed that the Bi0.75Ba0.25FeO3thin film was single phase with (1 0 1) preferential polycrystalline orientation. Both ferroelectricity and ferromagnetism of these films were observed at room temperature by P–E and M–H loop measurements, respectively. The magnetoelectric coupling effect was demonstrated by measuring the dielectric constant in a varying magnetic field. The dielectric constants measured at 10 kHz increased with an increase in the applied magnetic field, giving a coupling coefficient (εr (H) − εr (0))/εr (0) of 1.1% at H = 8 kOe at room temperature, which shows potential application.

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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.