Thickness-driven structure evolution and energy storage performance in epitaxial 0.88BaTiO3-0.12Bi(Mg0.5Ti0.5)O3 dielectric film

Ferroelectric film capacitors hold promise as energy storage devices in power systems, grid infrastructure, and electronic equipment. Herein, lead-free 0.88BaTiO3-0.12Bi(Mg0.5Ti0.5)O3 (BT-BMT) films with different thicknesses were fabricated on Nb:SrTiO3 substrates via radio frequency sputtering. By optimizing the film thickness, an effective trade-off between the film's crystallinity and size effect was realized, which significantly enhanced the breakdown strength of a 300-nm-thick film. Meanwhile, the reduced ratio of interfacial layers and the increased tetragonality with increasing thickness enable the 300-nm-thick BT-BMT film to exhibit the highest difference between the maximum polarization (Pm) and remanent polarization (Pr), with a Pm−Pr value of approximately ∼32 μC/cm2 at 4.0 MV/cm. The combination of the higher breakdown strength and the highest dielectric constant induces the energy storage density of ∼94 J/cm3 with an efficiency of up to ∼70% at room temperature. Furthermore, the optimized film exhibits a performance degradation of less than ∼3% after 106 charge-discharge cycles, and the operating temperature can be expanded to 200 °C, at which the energy storage density remained up to ∼79 J/cm3 with an efficiency of ∼75%, endowing it with strong practicality for energy storage applications. This work demonstrates that tailoring the thickness of energy storage dielectric films is an effective approach to improve their dielectric energy storage performance.