By reshaping nanoscale polarization inside a layered ferroelectric structure, researchers tested whether lead-free capacitors could store and release more energy without relying on extreme electric fields.
Paper: Superlattice Engineering in Relaxor Ferroelectric-based Capacitors for Ultra-Highly Efficient Recoverable Energy Storage Density. AI-generated abstract conceptual image created using ChatGPT/OpenAI
A recent study published in Nature Communications demonstrates how superlattice engineering can improve the energy-storage performance of lead-free relaxor ferroelectric capacitors.
The resulting capacitors achieved a recoverable energy-storage density of 12.6 J/cm³ at 920 kV/cm with an efficiency close to 99%. They delivered 20.4 J/cm³ at 1280 kV/cm with 86% efficiency and maintained stable energy-storage performance through 2 × 108 charge–discharge cycles under the tested conditions.
Engineering Relaxor Ferroelectrics for Efficient Energy Storage
Dielectric capacitors can store and release electrical energy rapidly, making them attractive for pulsed-power electronics and compact energy-storage systems.
Their performance depends on both recoverable energy storage density and efficiency. At a given field, high recoverable energy density favors a large difference between maximum polarization and polarization remaining after the field is removed, while high efficiency also requires low hysteretic losses. Achieving both properties remains challenging at low electric fields.
Relaxor ferroelectrics can help because they contain polar nanoregions (PNRs) and suppress long-range ferroelectric order. These regions can reorient under an electric field and become more randomly oriented after the field is removed, allowing polarization to return close to its initial state. This behavior can reduce hysteretic losses and improve energy-storage efficiency.
Many high-performance perovskite relaxor and ferroelectric thin films still require electric fields above 3 MV/cm to reach their highest reported energy densities.
The researchers address this limitation by engineering superlattices. They combine 0.5Ba(Zr0.2 Ti0.8)O3–0.5(Ba0.7Ca0.3)TiO3 (BCZT) with paraelectric SrTiO3 (STO) to form an epitaxial BCZT/STO superlattice. The resulting periodic structure changes the characteristic size and spatial organization of the PNRs.
The study examines how superlattice confinement and a strain-gradient-related imprint effect, a shift in the polarization response associated with an internal electric field, can improve both energy density and efficiency at comparatively low electric fields.
Designing and Characterizing the BCZT/STO Superlattice
The researchers fabricated 200 nm-thick BCZT films and BCZT/STO superlattices using pulsed laser deposition. In the superlattice, BCZT and STO layers were each about 15 nm thick, giving a bilayer periodicity of about 30 nm. The films were grown on single-crystal STO (001) substrates with a conductive La0.7Sr0.3MnO3 bottom electrode.
X-ray diffraction (XRD) confirmed the periodic superlattice structure through satellite peaks around the main Bragg reflections. High-angle annular dark-field scanning transmission electron microscopy revealed alternating BCZT and STO layers with sharp, coherent interfaces. Energy-dispersive spectroscopy (EDS) confirmed the expected elemental distribution and found no measurable cation interdiffusion beyond the technique's spatial resolution.
The researchers used complementary structural and electrical techniques to connect nanoscale structure with capacitor performance.
Second-harmonic generation measurements confirmed the polar character of the BCZT/STO superlattice. Four-dimensional scanning transmission electron microscopy revealed relative, depth-dependent lattice-distortion trends within the BCZT layers, including an interface-related structural gradient. The authors caution that these maps show spatial trends rather than exact absolute strain values. Atomic-resolution STEM measurements then mapped local B-site displacements to examine nanoscale polarization and PNR configurations.
The team also measured polarization–electric field loops, dielectric properties, breakdown strength, temperature-dependent behavior, and long-term cycling stability. These measurements let the researchers assess how superlattice confinement affected polarization reversibility, energy density, efficiency, and operational stability.
Nanoscale Polarization Enables High Energy-Storage Efficiency
The BCZT/STO superlattice showed a markedly different polarization response from the single-layer BCZT film. The BCZT film reached a maximum polarization of about 34 µC/cm² and retained 14 µC/cm² after the field was removed.
By comparison, the superlattice showed an ultra-slim polarization–electric field loop, with a maximum polarization of about 29 µC/cm² and almost no polarization remaining after field removal. Its coercive field also decreased from about 160 to 110 kV/cm.
Atomic-scale analysis provided evidence for the origin of this behavior. The superlattice produced fragmented nanoscale polarization configurations with a broader range of polarization orientations. The researchers attribute this change to confinement imposed by the periodic STO interfaces. Smaller and less spatially correlated PNRs can reorient more reversibly under an applied field while suppressing strong long-range ferroelectric order.
The authors also identify a depth-dependent lattice distortion, which they interpret as a substrate-induced strain gradient mainly associated with lattice mismatch near the BCZT/LSMO interface. They propose that this gradient modifies the built-in electric field and produces an imprint effect that further improves energy-storage performance.
The BCZT/STO superlattice achieved a recoverable energy-storage density of 12.6 J/cm³ at 920 kV/cm with efficiency close to 99%. Raising the field to 1280 kV/cm increased the recoverable energy-storage density to 20.4 J/cm³ at 86% efficiency.
The authors report that the recoverable energy-storage density and efficiency are about 40% higher than those of the single-layer BCZT film. The 1280 kV/cm result is close to the statistically measured breakdown field of 1342 ± 12 kV/cm, so it represents operation near the upper tested field range.
Toward Low-Voltage Lead-Free Energy-Storage Capacitors
The study shows that nanoscale superlattice design can improve the efficiency and recoverable energy density of lead-free dielectric capacitors at comparatively low fields.
The BCZT/STO architecture combines two mechanisms the authors identify. Confinement from the STO layers reduces the characteristic size of PNRs and the distance over which neighboring polar regions remain aligned, promoting more reversible polarization. A substrate-induced strain gradient near the BCZT/LSMO interface modifies the built-in electric field and contributes to the imprint effect. These mechanisms are associated with slim hysteresis and efficient energy release.
The resulting capacitor combined high recoverable energy density with strong efficiency across the tested field range. The device maintained stable energy-storage performance through 2 × 108 cycles and showed no obvious performance degradation up to 110 °C. The polarization–electric field loops became linear above about 85 °C, near the temperature of maximum dielectric permittivity.
These results distinguish the superlattice from conventional single-layer BCZT and many other lead-free ferroelectric thin-film systems.
The findings suggest that nanoscale control of polarization can improve dielectric energy storage without relying on the extreme electric fields used in many comparable thin-film systems. The BCZT/STO superlattice combines a lead-free composition with high efficiency, high recoverable energy density, and long cycling stability in the reported measurements.
The authors say the approach may also apply to other dielectric thin-film capacitors used in pulsed-power electronics and other miniaturized energy-storage technologies.
Disclaimer: The views expressed here are those of the author expressed in their private capacity and do not necessarily represent the views of AZoM.com Limited T/A AZoNetwork the owner and operator of this website. This disclaimer forms part of the Terms and conditions of use of this website.
Source:
- Oliveira, M. M. G. S., Jayakrishnan, A. R., et al. (2026). Superlattice engineering in relaxor ferroelectric-based capacitors for ultra-highly efficient recoverable energy storage density. Nature Communications. DOI: 10.1038/s41467-026-77971-6, https://www.nature.com/articles/s41467-026-77971-6