Capturing Carriers and Driving Depolarization by Defect Engineering for Dielectric Energy Storage

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 (Fe_Ti^' - V_o^••)^• and (Fe_Ti^″ - V_o^••) defect dipoles by oxygen vacancy defect engineering in acceptor doped Sr₂Bi₄Ti_(5-FeO₁₈ 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 Sr₂Bi₄Ti_4.92Fe_0.08O₁₈ 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.