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.

In this work, thick BiFeO₃ films (~1 μm) were prepared on LaNiO₃-buffered (111)Pt/Ti/SiO₂/(100)Si substrates via radio-frequency magnetron sputtering without post-growth annealing. The effects of the substrate temperature on the film’s crystallinity, defect chemistry, and associated electrical properties were investigated. In contrast to the poorly crystallized BiFeO₃ film deposited at 300 °C and the randomly-oriented and (111)-textured films deposited at 500 and 650 °C, respectively, a (001)-preferred orientation was achieved in the BiFeO₃ film deposited at 350 °C. This film not only showed a dense, fine-grained morphology but also displayed enhanced electrical properties due to the (001) texture and improved defect chemistry. These properties include a reduced leakage current (J ≈ 2.4×10⁻⁵ A/cm²@200 kV/cm), a small dielectric constant (ε_r ≈ 243–217) with a low loss (tanδ ≤ 0.086) measured from 100 Hz to 1 MHz, and a nearly intrinsic remnant polarization (P_r) of ~60 μC/cm². A detailed TEM analysis confirmed the R3c symmetry of the BFO films and hence ensured good stability of their electrical properties. In particular, single-beam cantilevers fabricated from BiFeO₃/LaNiO₃/Pt/Ti/SiO₂/Si heterostructures showed excellent electromechanical performance, including a large transverse piezoelectric coefficient (e_31,f) of ~−2.8 C/m², a high figure of merit (FOM) parameter of ~4.0 GPa, and a large signal-to-noise ratio of ~1.5 C/m². An in-depth analysis revealed the intrinsic nature of the e_31,f piezoelectric coefficient, which is well fitted along a straight line of e_31,f ratio = (ε_rP_r) ratio with the reported representative results. These high-quality lead-free piezoelectric films processed with a reduced thermal budget can open many possibilities for the integration of piezoelectricity into Si-based micro-electro–mechanical systems (MEMSs).

The excellent energy storage performances of dielectric materials, a high energy density and efficiency, the stability in a wide range of temperature, frequency and cycling time, are surely desirable for the energy storage devices. A trade-off relationship between polarization and breakdown strength, however, limits the enhancement of energy storage properties of dielectric materials. To effectively boost the energy density and efficiency of dielectric capacitors, by inserting a BiFeO₃ layer into the BaTiO₃ film in present case, the symmetric BaTiO₃/BiFeO₃/BaTiO₃ tri-layer film heterostructure with antiferroelectric-like characteristics was constructed based on the dual-interlayer coupling effect, what's more, its antiferroelectric-like characteristics will evolve with electric field. Such the tunable polarization behavior endows it with an enhanced maximum polarization but a reduced remnant one, a delayed saturation of polarization and a high breakdown strength, which are synergistically accountable for a large energy density (W_rec~109 J/cm³) and a high efficiency (η~82.6%), together with the good thermal (T_R~200 ℃, ΔW_rec<3% & Δη<10%) and frequency (50 Hz–10 kHz, ΔW_rec<7% & Δη<13%) stabilities, particularly an outstanding cycling reliability (10⁹ cycles, both ΔW_rec and Δη<1%). Hence these findings can provide some innovative ideas for enriching the performance tuning of ferroelectrics, especially in enhancing their energy storage characteristics.

Achieving an excellent energy storage performance, together with high cycling reliability, is desirable for expanding technological applications of ferroelectric dielectrics. However, in well-crystallized ferroelectric materials, the concomitant high polarizability and low polarization-saturation field have led to a square-shaped polarization–electric field loop, fatally impairing both recoverable energy density (W_rec) and efficiency (η). Nanocrystalline ferroelectric films with a macroscopically amorphous structure have shown an improved W_rec and η, but their much lower polarizability demands an extremely high electric field to achieve such performances, which is undesirable from an economic viewpoint. Here, we propose a strategy to boost the energy storage performances and stability of ferroelectric capacitors simultaneously by constructing a tri-layer film in which a well-crystallized ferroelectric layer was sandwiched by two pseudo-linear dielectric layers with a dominant amorphous structure. In sol–gel-derived BaTiO₃/(Pb,La,Ca)TiO₃/BaTiO₃ (BTO/PLCT/BTO) tri-layer films, we show that the above design is realized via rapid thermal annealing which fully crystallized the middle PLCT layer while left the top/bottom BTO cap layers in a poor crystallization status. This sandwiched structure is endowed with an enhanced maximum polarization while a small remnant one and a much-delayed polarization saturation, which corresponds to large W_rec ≈ 80 J/cm³ and high η ≈ 86%. Furthermore, the film showed an outstanding cycling stability: its W_rec and η remain essentially unchanged after 10⁹ electric cycles (ΔW/W < 4%, Δη/η < 2%). These good energy storage characteristics have proved the effectiveness of our proposed strategy, paving a way for the utilization of sandwiched films in applications of electric power systems and advanced pulsed-discharge devices.