Interlayer coupling to enhance the energy storage performance of Na_0.5Bi_0.5TiO₃-SrTiO₃ multilayer films with the electric field amplifying effect

Lead-free film dielectric capacitors with fast charge/discharge capability are very attractive for advanced pulsed power capacitors but lag behind in energy storage density. Here, simultaneously achieving high energy storage density and good thermal stability in a new lead-free relaxor ferroelectric multilayer film is proposed by combining the amplifying effect of electric field with interlayer coupling. The 0.7Na_0.5Bi_0.5TiO₃-0.3SrTiO₃ (0.7NBT-0.3ST) system with large polarization and 0.6SrTiO₃-0.4Na_0.5Bi_0.5TiO₃ (0.6ST-0.4NBT) system with high breakdown strength are chosen to form a multilayer film. On the one hand, in our previous work, it was demonstrated that these systems exhibit excellent energy performance. And due to the large difference in dielectric constants between the two systems, constructing multilayer films can realize the amplifying effect of electric field and then increase the breakdown strength. On the other hand, since the compositions of the two systems are similar, the dislocations at the interface can be significantly reduced. The results show that the multilayer films possess slim and tilted polarization-electric field hysteresis loops characterized by small remnant polarization and large maximum polarization. An ultrahigh energy storage density of 60 J cm^-3 is obtained under 2612 kV cm^-1 at room temperature in the 0.7NBT-0.3ST/0.6ST-0.4NBT multilayer film. Meanwhile, the new developed capacitor exhibits a wide temperature usage range between 20 and 180 °C, with less than 5% variation in energy storage density. These characteristics demonstrate that the 0.7NBT-0.3ST/0.6ST-0.4NBT multilayer film is a promising candidate for high-power energy storage applications.