Piezoelectric materials have been attracting wide research interest for decades due to their ability to interconvert mechanical and electrical energy. Various mechanisms from different perspectives have been proposed to explain high piezoelectricity; however, a unified framework across diverse perovskite piezoelectric systems remains elusive. Yao et al. introduced a concept termed fluctuating local polarization (FLP) as an effective index for high piezoelectricity in perovskite ferroelectrics. FLP describes the composition-dependent piezoelectric performance in individual solid solutions and also accounts for high piezoelectricity across distinct systems. The FLP metric integrates the magnitude of local electric dipoles and the disorder of their orientations. This concept does not supersede traditional viewpoints but rather rationalizes them under a common microscopic index: local polarization flexibility. FLP is not merely an explanatory fingerprint of high piezoelectricity; it can also serve as a practical reference for engineering the next generation of ferroelectric materials.

Potassium sodium niobate (KNN) lead-free piezoceramics are among the most promising candidates to replace lead-based counterparts. However, the limited temperature stability of KNN ceramics remains a critical challenge for practical application. This review provides a comprehensive overview of recent advancements in both the performance and temperature stability of KNN-based piezoceramics. Special emphasis is placed on the correlation between microstructure and temperature stability, with a systematic analysis of key strategies, including diffuse phase transition with multiphase coexistence, polar nanoregions, domain engineering, multilayer gradient doping structure, atomic-scale local ferroelectric state design, and defect engineering. Furthermore, an objective evaluation of these advances is provided to examine the potential mechanisms underlying these strategies. Beyond summarizing recent progress in improving the properties and temperature stability of KNN-based ceramics, this review highlights the intricate interplay between microstructure and piezoelectric performance, offering valuable insights to guide future research and the rational design of high-performance, temperature-stable KNN-based lead-free piezoceramics.

Dielectric materials are increasingly recognized as promising candidates for advanced energy storage and power amplification, particularly in dielectric capacitors that combine high power density with rapid charge-discharge capability and exceptional cycling stability. Special attention is given to the development of multilayer ceramic capacitors (MLCCs) for high-power pulsed systems, where the challenge lies in simultaneously achieving miniaturization and high energy density. This review highlights recent advances in dielectric materials, with particular emphasis on polarization engineering strategies that enhance energy and power densities through multiscale microstructural design, spanning devices, interfaces, grains, domains or nanoregions, and the lattice itself. Progress in material design is examined, including targeted doping, component solid solutions, high-entropy configurations, polarization mismatch, delayed polarization saturation, composite architectures, and texturing techniques, each evaluated for its role in improving dielectric performance. Special attention is devoted to solid-state dielectrics, which offer a unique combination of environmental compatibility and robust functional properties. The role of multiscale structural tailoring and processing innovations in optimizing dielectric responses is also explored. By integrating recent advances in polarization control and material design, this review outlines pathways toward next-generation dielectric energy storage systems, highlighting the importance of not only performance, but also scalability, reliability, and device integration.

All-solid-state batteries (ASSBs) promise high energy density and enhanced safety for electrochemical energy storage. The performance of dense composite cathodes relies on optimizing the phase fractions of cathode active material (CAM) and solid electrolyte (SE) to ensure effective electronic and ionic conduction, as well as sufficient interfacial contact. However, unavoidable porosity introduced during synthesis can compromise mass transport and interfacial kinetics, making it critical to predict optimal phase fractions in the presence of pores. Here, we present a computational framework for constructing an analytical surrogate model that captures complex microstructural effects, informed by numerical simulations of effective transport properties using over 250 virtual 3D microstructures. We systematically investigate the impact of phase fractions and porosity on effective diffusivity and the CAM-SE interfacial area. We report trends due to the differences in the diffusivities of widely studied CAM and SE materials. Our results indicate a tradeoff between achieving high effective ion diffusivity and maximizing specific interfacial area. The percolation threshold for lithium transport in the solid phase depends on the ratio of the diffusivity of the CAM phase to that of the SE phase. These simulation results are accurately described by analytical expressions derived from a nested generalized effective medium theory, offering a robust and practical predictive tool for optimizing composite cathode design in ASSBs.

The incorporation of metal species into two-dimensional (2D) carbon materials has emerged as a predominant strategy for designing advanced catalytic systems. Nevertheless, conventional metal-carbon hybrid catalysts frequently suffer from limited metal loading capacity and poor structural stability, significantly constraining their practical applications. By first-principles calculations, we predict a novel type of highly stable 2D atomically thin iron-carbon crystal. The designed 2D crystal has a chemical composition Fe₃C₁₈ with both FeC₃ and FeC₄ moieties in one unit cell. We show that the 2D-Fe₃C₁₈ can possibly be fabricated from a self-organizing process upon anchoring Fe atoms on 6,6,12-graphyne. The unique structure of 2D-Fe₃C₁₈ boasts a high Fe loading of 43.7 wt%, and also leads to high stability of the material at a temperature up to 1,000 K. Owing to the different coordination environments, different Fe atoms in 2D-Fe₃C₁₈ exhibit distinct electrocatalytic properties. The FeC₃ moiety is more active than FeC₄ for oxygen evolution reaction while the FeC₄ moiety is a better electrocatalyst than FeC₃ towards oxygen reduction reaction. These studies pave the way for the future design of new functional 2D metal carbides with variable structures.