Hui Liu

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 (Wrec) and energy storage efficiency (η) while also compromising energy storage stability. To address these challenges, a gradient nanocolumnar-crystallite-engineered BaTiO3/Ba(Zr0.2Ti0.8)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 (Pmax), a small remnant polarization (Pr), and a much-delayed polarization saturation, which account for a Wrec ≈ 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.

High‐energy‐density rechargeable batteries are plagued by electrode polarization, unstable interfaces, and parasitic side reactions, which severely restrict their electrochemical performance across diverse battery chemistries. Piezoelectric materials can construct dynamic built‐in electric fields via mechanical or electrochemical excitation, showing great potential to modulate ion migration, interfacial charge behavior, and reaction kinetics for optimized battery performance. In this review, we first outline the fundamental physical principles and material classification of piezoelectric materials, followed by a comprehensive summary of how the piezoelectric effect manifests differently when piezoelectric materials are integrated into a variety of battery components. Within electrode materials, piezoelectricity can accelerate interfacial ion diffusion, enhance redox reaction kinetics, and suppress undesirable side reactions through built‐in electric fields. On the anode side, the piezoelectric polarization field serves as an additional driving force to regulate ion flux and promote homogeneous metal deposition, thereby mitigating dendrite growth. In electrolytes and separators, piezoelectric materials can enhance ionic conductivity, stabilize electrode/electrolyte interfaces, and homogenize ion distribution, leading to improved electrochemical stability and reaction reversibility. Finally, current challenges and future perspectives are discussed to guide the rational design and practical implementation of piezoelectric‐enabled strategies for rechargeable energy‐storage systems featuring enhanced safety, prolonged service life, and high energy density.

The development of Pb-free dielectric materials with high recoverable energy-storage density (Wrec) and efficiency (η) remains a critical challenge for cutting-edge pulsed-power technologies. Herein, we propose a rational structural and chemical design to stabilize a relaxor state with tolerance factor t = 1.0096 by coupling highly distorted ferroelectric matrix with lattice-expanded component. We can disperse the strong long-range polarization within an expanded lattice framework through incorporating BaSnO3 into Bi0.5Na0.5TiO3-BaTiO3 solid-solution with significant ferroelectric polarization, thereby achieving a synergistic optimization between the large intrinsic polarization and lattice structure. Neutron total scattering combined with Reverse Monte Carlo modeling, and atomic-resolution displacement mapping reveal Sn4+ disrupts strong long-range polarization via B-site chemical frustration, generating polar nanoclusters with intense local distortions. Concurrently, Ba2+-driven lattice expansion enhances polarization flexibility under electric fields. Notably, Bi3+-enriched nanoregions retain unit-cell polarization up to 60 μC·cm-2, confirming the coexistence of relaxor dynamics and strong local polar fluctuations. The optimized ceramic exhibits slim hysteresis loops with exceptional energy-storage performance (Wrec = 11 J·cm-3, η = 85%), and excellent charge-discharge behavior (WD = 7.0 J·cm-3 and PD = 688 MW·cm-3). This work establishes a paradigm for correlating microstructure and performance in Pb-free relaxors with high capacitive energy-storage.

Dielectric capacitors are essential for high‐power, fast‐response electronics, but their performance is limited by trade‐offs between high polarization, low hysteresis loss, and high breakdown strength. The urgent need for eco‐friendly materials has spurred intense interest in lead‐free oxide dielectrics. Recent advances in synthesis and advanced characterization have revealed that atomic‐ and nanoscale local structures exert a profound influence on energy‐storage performance. Specifically, local polar nanoregions, chemical inhomogeneities, lattice distortions, and interfacial architectures play a pivotal role in regulating polarization configuration, leakage behavior, and breakdown pathways. This review systematically summarizes recent progress in lead‐free dielectric oxides through local structural design. After a concise overview of dielectric energy‐storage principles and classification, representative systems are discussed, with a focus on how specific local structural motifs correlate with macroscopic performance. The emerging strategies, such as local chemical framework design, high‐entropy approaches, polar nanodomain engineering, local microstructure architectures, multiphase/heterogeneous interfaces, and local amorphous design, are summarized. By integrating key advances in this field, the review clarifies intrinsic structure‐property relationships, identifies current challenges, and outlines opportunities for future breakthroughs, which could deliver timely guidance for designing high‐performance and environmentally benign dielectric capacitors.

Perovskite‐structured relaxor ferroelectrics have been extensively studied as dielectric energy‐storage capacitors, with applications across various electronics and electrical power systems. However, substantial improvements in energy‐density are typically hindered by early polarization saturation and a rapid decline in polarizability under high‐fields. To address this challenge, an atomic‐level design strategy is presented that integrates framework, ferroelectric‐active, rattling ions at A ‐site and insulating ions at B ‐site to induce a cooperative local polarization enhancement and rattling effects. Large‐scale simulations and local structure analysis based on neutron total scattering reveal that large‐sized framework ions enable local polarization enhancement of small ferroelectric‐active and rattling ions through size differences. Rattling ions, endowed with an expanded displacement space, heighten field‐driven polar extension, thereby slowing the reduction of polarizability under high‐fields. Guided by this strategy, (Ba _0.5 Bi _0.25 Na _0.25 )(Ti,Zr)O ₃ system is elaborately designed, which exhibits favorable polarization behavior featured with deferred polarization saturation and record‐high polarizability under an ultrahigh breakdown field. Consequently, the optimal composition demonstrates a giant energy density of 24.3 J cm ⁻³ with a high efficiency of 92.4%, outperforming current bulk ceramic capacitors. The work establishes a universal design paradigm for relaxor ferroelectrics toward next‐generation dielectric capacitors, and provides a theoretical framework for the chemical design of function‐orientated complex ferroelectrics.

Pb‐free relaxor ferroelectric (RFE)‐based dielectric capacitors have great potential in cutting‐edge pulsed‐power/high‐power systems. Particularly, a high energy density ( W _rec ) under a moderate electric‐field ( E ) is urgent for electric vehicles and advanced electronic devices. However, achieving this, such as overcoming the bottleneck of W _rec > 10 J cm ⁻³ under E ≤ 60 kV mm ⁻¹ , remains challenging owing to trade‐off between critical parameters. Herein, an adaptive local‐global structure tactic is presented to obtain large and high‐reversible polarizability, and realizing a record‐high W _rec of 12 J cm ⁻³ and a high efficiency ( η ) of 89% among Pb‐free bulk ceramics under moderate E . This is implemented by combining the strong distorted (Bi _0.5 Na _0.25 K _0.25 )TiO ₃ ferroelectric and paraelectric BaZrO ₃ to form global tolerance factor optimized solid‐solutions. Locally, such RFE state exhibits fluctuating atomic displacement vectors, featured by a broad range of magnitudes and orientations, and forming strongly polarizable and small‐sized clusters. It results in a record‐high reversible polarizability and large polarization difference of 56.3 µC cm ⁻² under 56 kV mm ⁻¹ . Furthermore, the excellent reliability, high discharge energy density (4.5 J cm ⁻³ ), and large power density (504.5 MW cm ⁻³ ) are obtained. These results demonstrate the feasibility of adaptive local‐global structure in enhancing the energy‐storage capabilities under moderate E .

Zero thermal expansion (ZTE) substances, whose volume remains invariant under temperature variations, have attracted significant attention owing to their extensive potential applications in advanced technology fields. However, practical challenges persist, including thermal expansion anisotropy, ferromagnetism, high density, and restricted ZTE temperature windows. In this study, we have achieved a lightweight, nonferromagnetic, isotropic ZTE in Yb(Al,Mn)₂ alloys, which exhibits continuous shiftability of the ZTE temperature window across a wide range (140-650 K). By employing multiple advanced experimental techniques and combining first-principles calculations, we have elucidated that the ZTE behavior originates from valence fluctuations accompanied by local structural distortions. The latter manifests as the first two observed effects: the splitting of local bond lengths and the attenuation of atomic displacements. More importantly, the induced enhancement of hybridization between Mn-3d and Yb-4f orbitals is identified as the primary mechanism responsible for the emergence of shiftability over a wide temperature range. This work presents an unprecedented phenomenon of continuously shiftable ZTE temperature windows observed in the mixed-valence system Yb(Al,Mn)₂, which holds significant potential for diverse thermal expansion control applications in advanced technological fields, paving the way for next-generation devices requiring exceptional dimensional stability. Furthermore, the modulation of valence fluctuations provides new strategies for the development of new ZTE materials in the future.

Understanding the atomistic mechanism underlying high piezoelectricity has long been a central focus in research of functional ferroelectric materials. Despite decades of research across various perovskite piezoelectric systems, a clear consensus on the underlying mechanisms remains elusive. We propose a new concept—fluctuating local polarization—a critical factor that effectively correlates with piezoelectricity and could serve as a generic fingerprint for enhanced piezoelectricity. This is achieved by quantitatively capturing the local polarization characteristics of 16 compositions from classical piezoelectric systems. Our findings show that greater fluctuating local polarization, considering both the magnitude and the orientation disorder of local polar displacement vectors, yields improved piezoelectric performance. High fluctuating local polarization value, corresponds to a reduced local potential energy stiffness, thereby facilitating polarization variations and resulting in an amplified piezoelectric response. The concept can further explain the performance gap between Pb-based and Pb-free ferroelectrics arising from the distinct A-site polar displacement characteristics. Overall, our concept offers an atomic-level insight into the enhanced piezoelectricity of perovskites and provides a theoretical framework for designing high-performance piezoelectric materials.

High-entropy tactics present exceptional promise in advancing the dielectric energy storage of relaxor ferroelectrics, thereby benefiting various pulsed-power electronic systems. However, their vast composition space poses challenges in the rational design of a high-performance system. Herein, we present a machine learning-supplemented strategy to design high-entropy relaxors, demonstrating an ultrahigh energy-storage density of 17.2 J cm^-3 and high efficiency of 87% at a high breakdown strength of 79 kV mm^-1. By integrating six A-site and one B-site critical intrinsic features of constituent ions, deduced from a constructed random forest regression model, the (Bi_2/5Na_1/5K_1/5Ba_1/5)(Ti,Hf)O₃ high-entropy system is identified. Atomic-level local structural analysis reveals that incorporating these certified cations, with diverse local polar and lattice construction characteristics, results in a highly fluctuating local polarization structure. This favorable structure is characterized by pronounced orientation disorder and a broadly distributed length of unit-cell polarization vectors within the expanded lattice framework. Macroscopically, the optimized relaxor displays high dielectric susceptibility and large resistance. Moreover, a large discharge energy density of 5.8 J cm^-3 and power energy density of 447 MW cm^-3, along with outstanding operational stability, are achieved. This study presents a data-driven model to explore complex intrinsic features and facilitate the design of high-performance relaxors.