Ferroelectric thin-film capacitors exhibit significant 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 co-optimization of recoverable energy density (W_rec) and efficiency (η), while also compromising energy storage stability. To address these challenges, a gradient nano-columnar crystallite engineered BaTiO₃/Ba(Zr_0.2Ti_0.8)O₃/BaTiO₃ sandwich film was constructed enabled via a low thermal budget process of 200 ℃. This approach facilitates an unique microstructure featured by gradient-distributed nano-columnar crystallites in the amorphous-dominated matrix via a spatially-separated manner throughout the sandwich film, thereby effectively modulating polarization behavior, mitigating dielectric nonlinearity, and consequently boost the energy storage performance remarkably. Experimental results demonstrate that this sandwiched structure is endowed with an enhanced maximum polarization (P_max) while a small remnant one (P_r), and a much-delayed polarization saturation, which are accountable 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 (RT~150℃) and frequency (100 Hz ~ 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 lays a foundation for those integrated energy storage devices.

Bi_0.5Na_0.5TiO₃–BaTiO₃ (BNT–100xBT) ceramics are promising candidates for piezoelectric applications. The correlation between their structure and piezoelectric properties has attracted considerable interest. Herein, the structures of 6BT and 7BT with distinct piezoelectricity are investigated via in-situ synchrotron X-ray diffraction and transmission electron microscopy. It is found that although both compositions present morphotropic phase boundary (MPB) features with coexisting R3c and P4bm phases, their refined structures are significantly different. 6BT is composed of the R3c phase with a small P4bm fraction after electrical poling, while 7BT presents comparable fractions of the two phases. Less pronounced structure distortion and oxygen octahedral tilting occur in 7BT, which favor the phase transformation, resulting in an enhanced piezoelectricity. This enhancement driven by structural flexibility is elucidated by phenomenological analysis. These results demonstrate that the design of high piezoelectricity at MPBs should consider not only the phase-coexisting states but also the refined crystal structure.