Ferroelectric (FE) ceramics with a large relative dielectric permittivity and a high dielectric strength have the potential to store or supply electricity of very high energy and power densities, which is desirable in many modern electronic and electrical systems. For a given FE material, such as the commonly-used BaTiO₃, a close interplay between defect chemistry, misfit strain, and grain characteristics must be carefully manipulated for engineering its film capacitors. In this work, the effects of grain orientation and morphology on the energy storage properties of BaTiO₃ thick films were systematically investigated. These films were all deposited on Si at 500 °C in an oxygen-rich atmosphere, and their thicknesses varied between ~500 nm and ~2.6 μm. While a columnar nanograined BaTiO₃ film with a (001) texture showed a higher recyclable energy density W_rec (81.0 J/cm³ vs. 57.1 J/cm³ @3.2 MV/cm, ~40% increase) than that of a randomly-oriented BaTiO₃ film of about the same thickness (~500 nm), the latter showed an improved energy density at a reduced electric field with an increasing film thickness. Specifically, for the 1.3 μm and 2.6 μm thick polycrystalline films, their energy storage densities W_rec reached 46.6 J/cm³ and 48.8 J/cm³ at an applied electric field of 2.31 MV/cm (300 V on 1.3 μm film) and 1.77 MV/cm (460 V on 2.6 μm film), respectively. This ramp-up in energy density can be attributed to increased polarizability with a growing grain size in thicker polycrystalline films and is desirable in high pulse power applications.

Here, we obtained a series of controllable thermal expansion alloys Tb_1-xEr_xCo₂Mn_y (x = 0-0.5, y = 0-0.4) by incorporating double rare earth doping and introducing non-stoichiometric Mn content. By varying the amount of Er or Mn, a low thermal expansion (LTE) is achieved in Tb_0.6Er_0.4Co₂Mn_0.1 (TECM, α₁ = 1.23 × 10^-6 K^-1, 125~236 K). The macroscopic linear expansion and magnetic properties reveal that anomalous thermal expansion is closely related to the magnetic phase transition. Synchrotron X-ray powder diffraction results show that TECM is a cubic phase (space group: Fd-3m) at high temperatures, and a structural transition to a rhombohedral phase (space group: R-3m) occurs as temperature decreases. The negative thermal expansion c-axis compensates for the normal positive thermal expansion of the basal plane, resulting in the volumetric LTE. This study provides a new metallic and magnetic ZTE material.

In this work, we developed three methods to map crystallographic variants of samples at the nanoscale by analyzing precession electron diffraction data using a high-temperature shape memory alloy and a VO₂ thin film on sapphire as the model systems. The three methods are (I) a user-selecting-reference pattern approach, (II) an algorithm-selecting-reference-pattern approach, and (III) a k-means approach. In the first two approaches, Euclidean distance, Cosine, and Structural Similarity (SSIM) algorithms were assessed for the diffraction pattern similarity quantification. We demonstrated that the Euclidean distance and SSIM methods outperform the Cosine algorithm. We further revealed that the random noise in the diffraction data can dramatically affect similarity quantification. Denoising processes could improve the crystallographic mapping quality. With the three methods mentioned above, we were able to map the crystallographic variants in different materials systems, thus enabling fast variant number quantification and clear variant distribution visualization. The advantages and disadvantages of each approach are also discussed. We expect these methods to benefit researchers who work on martensitic materials, in which the variant information is critical to understand their properties and functionalities.

Biomineralization is a process that leads to the formation of hierarchically arranged structures in mineralized tissues, such as bone and teeth. Extensive research has been conducted on the crystals in bones and teeth, with the aim of understanding the underlying mechanisms of the mineralization process. Pathological/ectopic mineralization, such as kidney stones, calcific tendinitis, and skeletal fluorosis, shares some similar features but different mechanisms to physiological mineralization. A better understanding will provide new perspectives for treating pathological/ectopic mineralization-related diseases. This review provides an overview of the mechanisms of the crystallization and growth of crystals in physiological and pathological conditions from a chemistry perspective. By linking the microstructures and functions of crystals formed in both conditions, potential approaches are proposed to treat pathological/ectopic mineralization-related diseases.

The two-dimensional (2D) materials offer atomic-level thickness and unique physical and chemical properties for the preparation of a new class of membranes, i.e., nanochannel membranes. The nanochannel membranes have been utilized in a broad spectrum of new separation applications. However, the instability of the nanochannels, interfacial instability of 2D materials, and the swelling problem could damage the membrane performance, such as permeability, selectivity, and service lifetime. Innovative strategies for constructing and regulating the nanochannels are enthusiastically explored to address these challenges. Along this line, in this work, we first provide insight into the mechanisms of the nanochannel construction, the separation mechanism, and the effect of nanochannels on the separation performance. Then, the strategies developed in the literature, in particular, the strategies for the preparation of ideal 2D nanosheets, the strategies for constructing nanochannels, and the strategies for regulating the characteristics of nanochannels (channel size, channel length, channel morphology, and channel surface physicochemical properties) are systematically summarized. After that, we briefly introduce the application of 2D-material-based nanochannel membranes and outline the current challenges and provide an outlook in the further exploration of separation mechanism, large-scale manufacturing, and the eventual commercialization of the membranes.

The high consumption of fossil energy has led to increasing concentrations of carbon dioxide (CO₂) in the atmosphere, making carbon capture and separation a research hotspot in this century. As novel porous materials, metal-organic frameworks (MOFs) are widely used for CO₂ capture due to their unique structures and tunable properties. Currently, several relatively mature strategies have been applied to synthesize MOFs for CO₂ capture. Herein, we investigate strategies for tuning the pore windows, pore sizes, open metal sites, and post-synthesis or pre-synthesis modifications of MOFs from the perspective of CO₂ capture performance. Furthermore, we summarize the relevant CO₂ capture technologies and research advances and describe the application of different strategies in the synthesis of CO₂ capture-oriented MOFs.

In thin samples, such as membranes, kinks inside ferroelastic domain walls interact through “dipolar” interactions following a 1/d² decay, where d is the distance between the walls. Simultaneously, the samples relax by bending. Bending is not possible in thick samples or can be suppressed in thin films deposited on a rigid substrate. In these cases, wall-wall interactions decay as 1/d, as monopoles would do. In free-standing samples, we show a wide crossover regime between “dipolar” 1/d² interactions and “monopolar” 1/d interactions. The surfaces of all samples show characteristic relaxation patterns near the kink, which consists of ridges and valleys. We identify the sample bending as the relevant image force that emanates from kinks inside walls in thin samples. When samples are prevented from bending by being attached to a substrate, the dipolar force is replaced by “monopolar” forces, even in thin samples. These results are important for transmission electron microscopy imaging, where the typical sample size is in the dipolar range while it is in the monopolar range for the bulk.

Researchers often improve the energy storage performance of NaNbO₃ ceramics through doping with Bi-based composites. Recent studies have shown that rare-earth elements, such as La and Sm, can suppress remanent polarization. In this study, a (1-x)NaNbO_3-xSm(Mg_0.5Zr_0.5)O₃ ceramic system was designed. Doping with Sm(Mg_0.5Zr_0.5)O₃ (SMZ) increases the resistance, activation energy, and bandgap of NaNbO₃ ceramics, improves the breakdown field strength, and optimizes the energy storage efficiency of NaNbO₃ ceramics. In this study, 0.92NaNbO₃-0.08 SMZ achieved an energy storage density of 4.3/cm³ and an energy storage efficiency of 85.6% at 560 kV/cm. When x = 0.15, the sample exhibited an ultrahigh breakdown field strength and energy storage efficiency (720 kV/cm and 91%, respectively). In addition, the 0.08 SMZ sample had an ultrafast release rate of t_0.9(57 ns), high current density (777.1 A/cm²), and high power density (69.93 MW/cm³). It has practical application prospects in high-performance energy storage capacitors.

BiFeO₃-BaTiO₃ (BF-BT)-based lead-free ceramics are promising piezoelectric materials exhibiting high Curie temperatures and excellent electrochemical properties. In this study, 0.70Bi_1+xFeO₃-0.30BaTiO₃ (B_1+xF-BT, x = -0.01, 0.00, 0.01, 0.02, 0.03, 0.04) lead-free piezoelectric ceramics were successfully fabricated via the conventional solid-phase reaction process. Crystallographic structure, microstructure, dielectric, impedance, ferroelectric, and piezoelectric properties among different compositions were comprehensively investigated. The X-ray diffraction analysis confirmed that all compositions exhibited a typical perovskite structure with a cubic-rhombohedral phase mixture. The grain size of ceramics tends to increase as the Bi₂O₃ content rises. In particular, the backscattered electron images and energy dispersive analysis revealed prominent core-shell microstructure within grains. Notably, the BF-BT ceramic containing 1% excess Bi displayed the maximum $$\ \large d_{33}$$ ~217 pC/N and $$\ \large d_{33}^{*}$$ ~243 pm/V accompanied by a high Curie temperature of 515 °C. The findings demonstrate the potential feasibility of BF-BT ceramics in the field of lead-free piezoelectric ceramics.

Precession electron diffraction (PED) is a powerful technique for revealing the crystallographic orientation of samples at the nanoscale. However, the quality of orientation indexing is strongly influenced by the quality of diffraction patterns. In this study, we have developed a novel algorithm called Auto-CLAHE (automatic contrast-limited adaptive histogram equalization), which automatically enhances low-intensity diffraction pattern signals using contrast-limited adaptive histogram equalization (CLAHE). The degree of enhancement is dynamically adjusted based on the overall intensity of the diffraction pattern, with greater enhancement applied to patterns with fewer spots (i.e., away from zone axes) and little or no enhancement applied to patterns with many spots (i.e., at a zone axis). By improving the visibility of low-intensity diffraction spots, Auto-CLAHE significantly improves the template matching between experimentally acquired and simulated diffraction patterns, leading to orientation maps with dramatically higher quality and lower noise. We anticipate that Auto-CLAHE provides an efficient and practical solution for preprocessing PED data, enabling higher-quality crystal orientation mapping to be routinely obtained.

In recent years, the rapid development of machine learning (ML) based on data-driven or environment interaction has injected new vitality into the field of meta-structure design. As a supplement to the traditional analysis methods based on physical formulas and rules, the involvement of ML has greatly accelerated the pace of performance exploration and optimization for meta-structures. In this review, we focus on the latest progress of ML in acoustic, elastic, and mechanical meta-structures from the aspects of band structures, wave propagation characteristics, and static characteristics. We finally summarize and envisage some potential research directions of ML in the field of meta-structures.

Seawater metal-air batteries (SMABs) are promising energy storage technologies for their advantages of high energy density, intrinsic safety, and low cost. However, the presence of such chloride ions complex components in seawater inevitably has complex effects on the air electrode process, including oxygen reduction and oxygen evolution reactions (ORR and OER), which requires the development of highly-active chloride-resistant electrocatalysts. In this review, we first summarized the developing status of various types of SMABs, explaining their working principle and comparing the battery performance. Then, the reported chlorine-resistant electrocatalysts were classified. The composition and structural design strategies of high-efficient chlorine-resistant ORR/OER electrocatalysts in seawater electrolytes were comprehensively summarized. Finally, the main challenges to be overcome in the commercialization of SMABs were discussed.

This article presents a vision for advancing the development of next-generation flame-retardant materials through the utilization of metal-organic frameworks (MOFs). The proposed vision is centered on four key areas: industrialization, multifunctionality, ligand synthesis, and derivatives. By optimizing production processes, customizing MOFs for specific properties and applications, and developing novel ligands and derivatives, the effectiveness and versatility of MOFs as flame-retardant materials can be significantly enhanced. This vision represents a promising direction for the field that has the potential to address critical safety concerns across various industries.

Scanning Transmission electron microscopy (STEM) technologies have undergone significant advancements in the last two decades. Advancements in aberration-correction technology, ultra-high energy resolution monochromators, and state-of-the-art detectors/cameras have established STEM as an essential tool for investigating material chemistry and structure from the micro to the atomic scale. This characterization technique has been invaluable for understanding and characterizing the origins of ferroic material properties in next-generation advanced materials. Many unique properties of engineering materials, such as ferroelectricity, piezoelectricity, and ferromagnetism, are intricately linked to their atomic-scale composition and structure. STEM enables direct observation of these structural characteristics, establishing a link with macroscopic properties. In this perspective, we provide an overview of the application of advanced STEM techniques in investigating the origin of ferroic material properties, along with discussions on potential opportunities for further utilization of STEM techniques.

Multiferroic materials, encompassing simultaneous ferroelectric and ferromagnetic polarization states, are enticing multi-state materials for memory scaling beyond existing technologies. Aurivillius phase B6TFMO (Bi₆Ti_xFe_yMn_zO₁₈) is a unique room temperature multiferroic material that could ideally be suited to future production of revolutionary memory devices. As miniaturization of electronic devices continues, it is crucial to characterize ferroelectric domain configurations at very small (sub-10 nm) thickness. Direct liquid injection chemical vapor deposition allows for frontier development of ultrathin films at fundamental (close to unit cell) dimensions. However, layer-by-layer growth of ultrathin complex oxides is subject to the formation of surface contaminants and 2D islands and pits, which can obscure visualization of domain patterns using piezoresponse force microscopy (PFM). Herein, we apply force from a sufficiently stiff diamond cantilever while scanning over ultrathin films to perform atomic force microscopy (AFM)-based nano-machining of the surface layers. Subsequent lateral PFM imaging of sub-surface layers uncovers 45° orientated striped twin domains, entirely distinct from the randomly configured piezoresponse observed for the pristine film surface. Furthermore, our investigations indicate that these sub-surface domain structures persist along the in-plane directions throughout the film depth down to thicknesses of less than half of an Aurivillius phase unit cell (< 2.5 nm). Thus, AFM-based nano-machining in conjunction with PFM allows demonstration of stable in-plane ferroelectric domains at thicknesses lower than previously determined for multiferroic B6TFMO. These findings demonstrate the technological potential of Aurivillius phase B6TFMO for future miniaturized memory storage devices. Next-generation devices based on ultrathin multiferroic tunnel junctions are projected.

Magnetic hyperthermia uses magnetic nanoparticles (MNPs) for conversion of magnetic energy into thermal energy under an alternating magnetic field (AMF) to increase local temperature for ablation of cancer cells. The magnetic thermal capacity of MNPs not only depends on the intrinsic properties of MNPs but is also affected by the microenvironmental matrices surrounding the MNPs. In this study, the influence of agarose hydrogels and gelatin porous scaffolds on the magnetic thermal property and anticancer effect of Fe₃O₄ nanoparticles (NPs) were investigated with a comparison to free Fe₃O₄ NPs. Flower-like Fe₃O₄ NPs were synthesized and embedded in agarose hydrogels and gelatin porous scaffolds. Under AMF irradiation, the free Fe₃O₄ NPs had the best magnetic thermal properties and the most efficiently increased the local temperature to ablate breast cancer cells. However, the Fe₃O₄ NPs embedded in agarose hydrogels and gelatin porous scaffolds showed reduced magnetic-thermal conversion capacity, and the local temperature change was decreased in comparison to free Fe₃O₄ NPs during AMF irradiation. The gelatin porous scaffolds showed a higher inhibitory influence than the agarose hydrogels. The inhibitory effect of agarose hydrogels and gelatin porous scaffolds on magnetic-thermal conversion capacity resulted in a decreased anticancer ablation capacity to breast cancer cells during AMF irradiation. The Fe₃O₄ NP-embedded gelatin scaffolds showed the lowest anticancer effect. The results suggested that the matrices used to deliver MNPs could affect their performance, and appropriate matrices should be designed to maximize their therapeutic effect for biomedical applications.

Cryogenic atom probe tomography (cryo-APT) is a new microstructure characterization technique with the potential to address challenges across various research fields. In this review, we provide an overview of the development of cryo-APT and the associated instrumentation that transforms conventional APT into cryo-APT. We start by introducing the APT principle and the instrumentation involved in the cryo-APT workflow, emphasizing the key techniques that enable cryo-APT specimen preparation. Furthermore, we shed light on the research made possible by cryo-APT, presenting several recent outcomes to demonstrate its capabilities effectively. Finally, we discuss the limitations of cryo-APT and summarize the potential research areas that can further benefit from this cutting-edge microstructural characterization technique.

Compounds with perovskite structures have become one of the focuses in both materials science and condensed matter physics because of their fascinating physical properties and potential functionalities correlated to magnetic structures. However, the understanding of the intriguing physical properties is still at an exploratory stage. Herein, owing to the magnetic frustration prompted by Mn₆N or Mn₆C octahedra, the abounding magnetic structures of antiperovskites, including collinear antiferromagnetic, collinear ferromagnetic, collinear ferrimagnetic, non-collinear magnetic, and non-coplanar magnetic spin configurations, are systematically introduced through the updated coverage. In addition, owing to the “spin-lattice-charge” coupling of antiperovskites, a large number of physical properties, such as anomalous thermal expansion, giant magnetoresistance, anomalous Hall effect, piezomagnetic/baromagnetic effects, magnetocaloric effect, barocaloric effect, etc., are summarized by combining the discussions of the determined magnetic structures. This review aims to clarify the current research progress in this field, focusing on the relationship between the magnetic structures and the correlated physical properties, and provides the conclusion and outlook on further performance optimization and mechanism exploration in antiperovskites.

In many commercially utilized ferroelectric materials, the motion of domain walls is an important contributor to the functional dielectric and piezoelectric responses. This paper compares the temperature dependence of domain wall motion for BaTiO₃ ceramics with different grain sizes, point defect concentrations, and formulations. The grain boundaries act as significant pinning points for domain wall motion such that fine-grained materials show smaller extrinsic contributions to the properties below the Curie temperature and lower residual ferroelectric contributions immediately above the Curie temperature. Oxygen vacancy point defects make a modest change in the extrinsic contributions of undoped BaTiO₃ ceramics. In formulated BaTiO₃, extrinsic contributions to the dielectric response were suppressed over a wide temperature range. It is believed this is due to a combination of reduced grain size, the existence of a core-shell microstructure, and a reduction in domain wall continuity over the grain boundaries.

Single crystals of 0.7Pb(Mg_1/3Nb_2/3)O₃-0.3PbTiO₃ (PMN-30PT) with a composition close to the morphotropic phase boundary have demonstrated remarkable electromechanical properties, stimulating intensive research interest in the field of piezoelectrics. Domain structures have long been associated with their overall piezoelectric properties, thereby garnering particular research interest for the enhancement of piezoelectric properties. Here, we report on three distinct domain structures in this material. Through a combination of X-ray diffraction reciprocal space mapping and piezoresponse force microscopy measurements, an M_A crystal structure has been confirmed. The three-dimensional polar vectors of the three domain structures have been reconstructed with two 4M_A and one 2M_A domain structures. Correlations between different domain structures and their local electrical switching properties have been revealed. Our study of the PMN-30PT single crystal examines diverse domain structures at the mesoscale in detail, which provides valuable insight into the relationship between structures and properties of the material.