Gradient nano-columnar crystallite engineering-enabled BaTiO₃/Ba(Zr_0.2Ti_0.8)O₃/BaTiO₃ sandwich films with superior energy storage performance via a low thermal budget

Ferroelectric thin-film capacitors exhibit significant potential for applications in pulsed power systems due to their high power density and ultrafast charge/discharge capability. However, the inherent trade-off between polarization and breakdown strength in ferroelectrics fundamentally imposes challenges for the co-optimization of recoverable energy density (W_rec) and energy storage efficiency (η) while also compromising energy storage stability. To address these challenges, a gradient nanocolumnar-crystallite-engineered BaTiO₃/Ba(Zr_0.2Ti_0.8)O₃/BaTiO₃ sandwich film was constructed via a low thermal budget process at 200 °C. This approach facilitates a unique microstructure featuring gradient-distributed nanocolumnar crystallites in an amorphous-dominated matrix in a spatially separated manner throughout the sandwich film, thereby effectively modulating polarization behavior, mitigating dielectric nonlinearity, and consequently boosting the energy storage performance remarkably. Experimental results demonstrate that this sandwiched structure is endowed with an enhanced maximum polarization (P_max), a small remnant polarization (P_r), and a much-delayed polarization saturation, which account for a W_rec ≈ 100.6 J/cm³ with an ultrahigh η ≈ 90.9% at 6.1 MV/cm. Furthermore, these sandwich films displayed broad operating temperature (room temperature to 150°C) and frequency (100 Hz to 10 kHz) stability and especially robust cycling reliability (2×10⁹ cycles). Through an innovatively engineered sandwich heterostructure design coupled with a low thermal budget, simultaneous achievements of low-temperature compatibility and superior energy storage characteristics lay a foundation for integrated energy storage devices.