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.

Conventional rigid reinforcing particles in metal matrix composites (MMCs) typically induce limited or single-level hetero-deformation induced (HDI) strengthening and hardening effect, thereby restricting the further enhancement of mechanical properties. We propose to incorporate deformable reinforcing particles (e.g., medium-/high-entropy materials) into metallic matrices to overcome the above limitation, and verify the feasibility in the laser powder bed fusion of VNbMoTa-reinforced Inconel 625 composites. The VNbMoTa particles demonstrated superior storage capacity for geometrically necessary dislocations, triggering significant HDI effects and resulting in excellent room- and elevated-temperature tensile properties. It is encouraging that the HDI effect arises between the deformable particles and the matrix, distinct from the current method of generating HDI effects among different parts of the matrix. This innovative strategy enlightens that deformable reinforcing particles are conducive to activating multi-level HDI effects in MMCs through coordinated interactions among reinforcing particles and matrix for better mechanical properties.

Driven by the rapid advancement of key engineering domains such as aerospace, transportation, and marine systems, there is an urgent need for aluminum alloys exhibiting superior mechanical properties. Heterostructures, defined by inhomogeneous distributions of microstructural domains with distinct property gradients, have become a leading strategy to achieve a synergy between outstanding strength and satisfactory ductility. Additive manufacturing technologies, particularly laser powder bed fusion (L-PBF), provide unparalleled design flexibility for creating heterogeneous microstructures. This review systematically classifies the various heterostructures in additively manufactured aluminum alloys, investigates the mechanisms enabling precise control of microstructural heterogeneity, and underscores the exceptional mechanical performance of L-PBF-processed alloys with such structures. Moreover, the challenges and opportunities associated with advancing heterostructured aluminum alloys via L-PBF are critically analyzed, highlighting the necessity for robust theoretical frameworks and scalable manufacturing approaches.

Internal defects, especially those caused by elemental segregation and minor phases in as-cast super-thick steel plates with large section sizes, can critically impact the subsequent manufacturing processes and the mechanical properties of final products, which may result in catastrophic failure during industrial applications. However, the effects of elemental segregation and the resultant phase structures on deformation behaviors and real-time microstructural evolution under tensile loading remain unexplored in as-cast super-thick steels. In this study, we employed in-situ synchrotron and neutron diffraction techniques during tensile tests to investigate the relationship between internal defects and deformation behaviors of segregated and non-segregated super-thick steels. Compared to the segregated sample, the non-segregated sample exhibited improved yield and tensile strengths, increasing from 407.5 and 590.5 MPa to 515.2 and 632.8 MPa, respectively, with a significant increase in elongation from 8% to 23.4%. Strip-like elemental segregations were observed in the central core area due to final solidification, and the stress partitioning between ferrite matrix and retained austenite was revealed to be beneficial for uniform plastic deformation and necking before fracture. Both ductile and brittle fractographies were identified in segregated conditions. Our findings address a critical knowledge gap in understanding how elemental segregation and minor phases affect deformation behaviors, and offer valuable insights for optimizing processing parameters for as-cast super-thick steels.

Machinable layered ternary carbides and nitrides (MAX phases) are a class of multifunctional materials combining the advantages of both ceramics and metals, making them of vital technological importance. Understanding their mechanical behavior is critical for practical applications and failure analysis. However, there is still no in situ investigation on their strength and plastic deformation under high pressure/stress. In this study, we investigate the strength and texture development of Ti₃AlC₂ under nonhydrostatic pressure up to 41 GPa. Clear strength anisotropy was observed and the lattice stress states of different planes were determined. At 41 GPa, the highest differential stresses supported by the (10-10) plane and (0008) plane are approximately 13.7 GPa and 4.5 GPa, respectively. The average strength exceeds that of stishovite, one of the strongest oxides. A strong 0001 deformation texture developed under ultra-high stress. This work clearly reveals the lattice-stress states and deformation behavior of Ti₃AlC₂ under high stress, offering direct experimental insights for the design and processing of MAX phase materials.

Aqueous zinc ion batteries have emerged as promising candidates for next-generation energy storage systems due to their inherent advantages of cost-effectiveness, operational safety, and environmental compatibility. Nevertheless, critical challenges including zinc dendrite formation, parasitic corrosion reactions, hydrogen evolution, and unsatisfactory Zn²⁺ diffusion kinetics still hinder their commercial viability. To address these limitations systematically, recent research efforts have focused on developing comprehensive mechanistic analyses through advanced characterization methodologies. This review presents a critical evaluation of state-of-the-art analytical techniques for investigating aqueous zinc ion batteries, encompassing fundamental principles, operational protocols, and practical applications across various research scenarios, thereby establishing a robust methodological framework for future studies. The discussion commences with an examination of conventional characterization approaches that provide essential baseline information regarding electrode morphology and electrochemical behavior. Subsequently, we introduced in situ analytical platforms combining three-dimensional visualization techniques, multimodal spectroscopic characterization, and dynamic electrochemical monitoring systems. These advanced operando characterization tools enable real-time observation of interfacial evolution and transient reaction processes, offering unprecedented insights into battery failure mechanisms at multiple scales.

The oxygen reduction reaction (ORR) is a clean energy conversion process with the potential to address the current energy crisis and promote the adoption of clean energy sources. Developing high-activity catalysts is essential to accelerate the inherently slow ORR kinetics and improve overall efficiency. Atomic-level oxygen reduction catalysts can be prepared through pyrolysis and solvothermal synthesis, using metal-organic frameworks (MOFs) as precursors or templates. This approach preserves the structural advantages of MOFs while enabling precise, atomic-scale tuning of catalyst composition and structure, thereby optimizing their ORR catalytic performance. Advances in catalyst synthesis and characterization methods have improved the understanding of the dynamic evolution of active centers and ORR performance in real-world devices. This paper provides a comprehensive review of ORR mechanisms, describes MOF-derived ORR catalytic materials with distinct ligands, and classifies them by ligand type to elaborate on the role of ligands in catalyst derivation and their influence on ORR performance. It further discusses the tuning of various MOF-derived catalyst types-single-atom, dual-atom, and cluster configurations-through precise control of metal content and species, exploring the relationship between catalyst architecture and ORR activity. The challenges of real-time monitoring of MOF pyrolysis and of understanding dynamic metal coordination during catalytic processes are also discussed. Finally, it examines the future prospects and challenges of MOF-based catalysts for the ORR.

Traditional homogeneous copper alloys often exhibit a significant reduction in electrical conductivity upon enhancement of mechanical strength, creating a strength-conductivity trade-off. The development of heterostructured copper alloys through the introduction of non-uniform microstructural features, including grain size gradients, nano-twin distributions, and layered heterostructures, offers a novel strategy to overcome this limitation. This review systematically examines the design principles, preparation technologies, and performance regulation mechanisms of heterostructured copper alloys, with a focus on analyzing the research progress of three representative heterostructured systems: gradient structures, layered structures, and dual-phase structures. It is demonstrated that heterostructured copper alloys significantly improve strength and ductility through mechanisms such as Geometrically necessary dislocations-induced back-stress effects, heterogeneous deformation-induced hardening, and cross-scale synergistic interactions. Additionally, the synergy between heterogeneous grain size and precipitates enables an optimized balance between strength and electrical conductivity. In layered heterostructured systems, interfacial stress modulation and microcrack deflection mechanisms enhance fracture toughness and thermal conductivity. Furthermore, the synergistic interaction between two phases in dual-phase structures refines the strength-ductility balance of conventional materials and expands the potential for functionalized design. This review aims to elucidate the microscopic mechanisms underlying various high-strength, high-conductivity heterostructure strengthening strategies in copper alloys, provide theoretical support for multi-scale design and performance regulation of heterostructured systems, and facilitate their large-scale application in new energy technologies, electronic devices, and other fields.

Nanocarbon materials, especially carbon nanotubes and graphene, have become preferred reinforcements for advanced aluminum (Al) matrix composites due to their excellent physical and mechanical properties. However, the strength-ductility trade-off in nanocarbon/Al composites remains a major obstacle to their engineering applications. Recent research has shown that heterogeneous design, aimed at promoting uniform strain distribution, enables nanocarbon/Al composites to maintain high strength while significantly improving their ductility. This work reviews recent research advances in heterostructured nanocarbon/Al composites, focusing on their fabrication, mechanical properties, fatigue damage behaviors, and hot processing characteristics. By addressing the critical scientific issues spanning from fabrication to service performance, this review aims to provide a theoretical foundation for developing high-performance heterostructured nanocarbon/Al composites and hasten their engineering applications.