Three-dimensional (3D) topological magnetic structures have attracted enormous interest due to their exceptional spatial structures and intriguing physics. Hopfions, characterized by the Hopf index, are 3D spin textures that emerged as closed twisted skyrmion strings. A comprehensive understanding of magnetic structural transitions within nanostructures is crucial for their applications in spintronics devices. Despite the demonstration of stabilization and current-driven dynamics of hopfion, their behavior in geometric confinement has remained unexplored. Here, we investigate the transformation between hopfions and torons in various nanostructures using micromagnetic simulations. By tailoring the axial ratio of elliptical nanodisks, the elliptical hopfion is found to be transformed into a toron structure. Moreover, the current-driven topological transformation between hopfion and toron has also been realized in finite-sized nanostripes and stepped nanostructures. This deformation and transformation arise from the repulsive potential of the boundaries or edges. To connect real-space observations and 3D topological spin configurations, we simulate the Lorentz transmission electron microscope images of the aforementioned magnetic structures. This study, uncovering the dynamics and transformation of hopfions, will invigorate 3D magnetic structures-based memory and logic devices.

Materials with negative/zero area compressibility (NAC or ZAC), which expand or keep constant along two directions under hydrostatic pressure, are very rare but of great scientific and engineering merits. Here, we investigate “wine-rack” architecture, which is the most prevailing for the pressure-expansion effect in materials, and identify that two allotropes (Ag₃BO₃-I and -II) of Ag₃BO₃ have the ZAC and NAC effects, respectively, by the first-principles calculations. Structural analysis discloses that the competition between the contraction effect from the bond length/angle shrinkage and the expansion effect from the angle closing between O-Ag-O bars and the (a, b) plane dominates the occurrence of ZAC/NAC, and the framework openness governs the competing balance in this system. This work deepens the understanding of “wine-rack” models and enriches the NAC/ZAC family.

Lithium (Li)-ion batteries have become one of the main energy sources for electric vehicles and energy storage systems, which puts forward higher requirements for the detection of battery state of health (SOH). The SOH of batteries is crucial for areas such as battery management and renewable energy storage. Accurately evaluating the SOH of batteries can optimize charging and discharging strategies and extend battery life. Therefore, accurately and effectively monitoring the SOH of Li batteries is of great significance. An ultrasonic testing technology has been proposed that can non-destructively test the Li battery SOH, enabling accurate judgment of batteries in poor or damaged conditions. Firstly, the hetero-structured MnO₂-Au has been constructed as the anode for Li-ion batteries. MnO₂-Au heterojunction enhances electronic conductivity and ion conductivity. The MnO₂-Au has exhibited high specific capacity and superior rate performances, which can well satisfy the ultrasonic inspection of the battery. Then, the ultrasonic testing has been conducted on batteries with different ages. The results suggest that batteries with short circuits have the highest nonlinear coefficient, while batteries with short circuits after long cycles have the lowest nonlinear coefficient. The nonlinear coefficient of batteries with different charging and discharging states is in the middle.

Ferroelectric thin films with high index orientations are found to possess unique structures and properties. In this work, we constructed the misfit strain-misfit strain phase diagram of (110)-oriented PbTiO₃ (PTO) thin films by phase-field simulations. The evolutions of ferroelectric phase structures, domain morphologies, volume fractions, and polarization components with the anisotropic strains were analyzed in detail. Large anisotropic strains exist between the orthorhombic scandate substrates and (110)-oriented PTO films, which makes it possible to engineer the structures and properties by anisotropic strain. These results deepen the understanding of ferroelectric domain structures of (110)-oriented PTO films under the anisotropic strain and provide theoretical support for the anisotropic strain engineering of high-index thin films experimentally.

The current boost in the search for energy-efficient device paradigms motivates the integration of materials with coexisting and coupled electric and magnetic order parameters into application-relevant architectures. In the so-called multiferroic magnetoelectrics, the understanding of switching events, however, is most of the time obstructed by the complex physics involved and in the non-trivial domain and domain wall configurations. This perspective offers an insightful overview of the most recent progress in the non-invasive optical probe of technology-significant ferroelectricity and antiferromagnetic order: the optical second harmonic generation (SHG). Over the last decade, its use in materials science has evolved, and SHG now enables the monitoring of the emergence of polarization in thin films, even during the epitaxial deposition process. Its long working distance further expedites the probe of multiple order parameters in various environments and under multi-stimuli excitations. The potential for the probe of complex electric dipole textures, such as ferroelectric skyrmions and time-resolved measurements, using SHG-based approaches in the most recent materials systems will be discussed.

Freckles, one of the common defects in blades used in heavy-duty gas turbines, hugely deteriorate the mechanical properties and liability of blades under service conditions. The thermal-solutal convection theory is a widely adopted formation mechanism, but few solid experimental pieces of evidence have been reported. Here, the grain microstructure in freckle chains taken from four different Nickel-based superalloys with either single-crystal or directionally solidified alloy is analyzed for the first time. The relationship between the internal stress and the misorientation throughout the freckle chains is studied by means of state-of-the-art electron microscopy. The results supply new experimental evidence of the thermal-solutal convection theory, which is further supported by the fact that borides at the boundary are randomly orientated to alloys. Therefore, this research enriches the methodology of freckle study, providing new insight into the formation mechanism of casting defects.

Commercial nonvolatile Ferroelectric Random Access Memory employs a destructive readout scheme based on charge sensing, which limits its cell scalability in sizes above 100 nm. Ferroelectric domain walls are two-dimensional topological interfaces with thicknesses approaching the unit cell level between two antiparallel domains and exhibit electrical conductivity, distinguishing them from insulating matrices that are uniformly ordered. Recently, novel research has been devoted to utilizing this extraordinary interface for the application in nonvolatile memory with nanometer-sized scalability and low energy consumption. Here, we pay more attention to the development of the domain wall memory technologies in the future with challenges and opportunities to design planar and vertical arrays of the memory cells in the CMOS platform.

Photocatalysis (PC) and photoelectric catalysis (PEC) are environmental protection technologies that use sunlight capacity and environmental governance, and they have a wide range of applications in hydrogen production, carbon dioxide reduction, organic degradation, and other fields. When the light is irradiated on the material, part of the light energy will be converted into heat energy, and the combination of this part of the heat energy with PC and PEC will become an important way to improve optical performance. Compared with traditional technology, the synergistic effect of light and heat can obtain higher catalytic performance and improve energy utilization efficiency. This review begins with an overview of the principle of photoheat generation, which produces heat energy in a non-radiative process through photo-induced instability of electrons. The principle of thermal effect on the performance improvement of PC/PEC is analyzed from the dynamics and thermodynamics of photoreaction and electric reaction. On this basis, several materials widely used at present are listed, such as oxides, plasmas, conductive polymers, carbon materials, and other typical photothermal materials. The specific applications of photothermal materials in PC and PEC processes, such as hydrogen production by oxidation, carbon dioxide reduction, organic matter reduction, and seawater desalination, were discussed. Finally, the challenges to PC/PEC from the introduction of thermal effects are further discussed to provide a clean and sustainable way to build a carbon-neutral society.

Based on statistical mechanics, a macroscopically homogeneous system, i.e., a single phase in the present context, is composed of many independent configurations that the system embraces. The macroscopical properties of the system are determined by the properties and statistical probabilities of those configurations with respect to external conditions. The volume of a single phase is thus the weighted sum of the volumes of all configurations. Consequently, the derivative of the volume to temperature of a single phase depends on both the derivatives of the volumes of every configuration to temperature and the derivatives of their statistical probabilities to temperature, with the latter introducing nonlinear emergent behaviors. It is shown that the derivative of the volume to the temperature of the single phase can be negative, i.e., negative thermal expansion, due to the symmetry-breaking non-ground-state configurations with smaller volumes than that of the ground-state configuration and the rapid increase of the statistical probabilities of the former, and negative thermal expansion can be predicted without fitting parameters from the zentropy theory that combines quantum mechanics and statistical mechanics with the free energy of each configuration predicted from quantum mechanics and the partition function of each configuration calculated from its free energy.

Diamond and cubic boron nitride (BN) are important materials with a variety of technological and industrial applications; however, overcoming the intrinsic brittleness of these materials is still a challenge. Here, we synthesize a compound of crystalline BN and amorphous diamond-like carbon through BN nanotubes and fullerene under high pressure and high temperature conditions. The obtained composite exhibits excellent combination of a measured Vickers’ hardness of 86.2 GPa and fracture toughness of 10.2 MPa m^1/2. Morphological and structural characterizations reveal that the amorphous diamond-like carbon is homogeneously embedded in a matrix of dense BN. The formation of the amorphous diamond-like carbon particles within the polycrystalline BN can effectively impede the migration of crack tips when the compound is cracking, in which most of crack tips are forced to deflect or confined near the boundaries of dense BN and amorphous diamond particles. The crystalline-amorphous composite strengthening presented here may provide a promising strategy for the further improvement of mechanical properties of hard or superhard materials.

The field of magnetic functional materials continues to garner significant attention due to its research and diverse applications, such as magnetic storage and spintronics. Among these, La(Fe,Si/Al)₁₃-based materials exhibit abundant magnetic properties and emerge as highly captivating subjects with immense potential. This review provides an overview of the diverse magnetic structures and itinerant electron metamagnetic transition observed in La(Fe,Si/Al)₁₃-based materials. The transformation of different magnetic configurations elicits the phenomena such as negative thermal expansion, magnetostriction, magnetocaloric effect, and barocaloric effect. In addition, the pivotal role of spin and lattice coupling in these phenomena is revealed. The magnetic functionalities of La(Fe,Si/Al)₁₃-based materials can be controlled through adjustments of magnetic exchange interactions. Key methods, including chemical substitution, external field application, and interstitial atom insertion, enable precise modulation of these functionalities. This review not only provides valuable insights into the design and development of magnetic functional materials but also offers significant contributions to our understanding of the underlying mechanisms governing their magnetic behaviors.

Owing to their unique compositional and structural characteristics, layered van der Waals solids in binary and ternary chalcogenide families provide a fertile testbed for exploring novel exotic structures and states, e.g., topological insulators and superconductors. Herein, a comprehensive study on the structural variations and correlated electrical transport behavior of SnSb₂Te₄, a ternary member, has been carried out considering elevated pressures. Under 45.6 GPa, three distinct structural phase transitions have been observed, with strong evidence from the variations of high-pressure X-ray diffraction patterns. The onsets of phase II (monoclinic, C2/m) at 6.3 GPa, phase III (monoclinic, C2/c) at 15.5 GPa, and phase IV (body-centered cubic with substitutional disorder, Im-3m) at 17.2 GPa have been observed owing to the emergence of new diffractions. Based on electrical measurements at low temperature and high pressure conditions, two pressure-induced superconducting states have been distinguished in SnSb₂Te₄. The first state occurs in the range of 12.3-17.1 GPa. The positive pressure dependence on Tc indicates that the aforementioned state is related to the monoclinic C2/m phase. At > 17.1 GPa, the second superconducting state emerges, with the negative pressure dependence on Tc. It relates to the body-centered cubic solid solution phase, which is characteristic of a substitutional disordered crystal structure. The discovery that the pressure-induced superconductivity in SnSb₂Te₄ is affected by structural phase transitions under pressure may help understand the universal relationship between the ambient condition topological insulating state and derived superconductivity. Ab initio theoretical calculations reveal that an electronic topological transition takes place at approximately 2.0 GPa, which is featured by the obvious changes in the distribution of electronic density of states near the Fermi level.