The classic auxetic perforated sheets with diamond-shaped voids reproducing the rotating-square topology are re-investigated and optimised via the incorporation of additional triangular voids at the edges of each diamond perforation. The scope is to make these systems lighter and render their pores more suitable for applications that require particular geometric features. Results show that the addition of such small- to medium-sized triangular voids did not have much effect on the extent of auxetic behaviour compared to the equivalent system having just diamond-shaped voids. This is rather remarkable given the very noticeable change in pore shape and size and the reduction in solid material and density. We also show that the exact magnitude of the Poisson's ratio may be fine-tuned through careful choice of various geometric parameters. All this broadens the potential of perforated auxetic systems for lightweight structural design and applications where specific pore geometries are required.
This article identifies and analyzes a new class of metamaterials that exhibit a previously unreported pseudo-bifurcation of on-axes Poisson's ratios. The metamaterials consist of rotating rhombic units, each composed of four triangular or trapezoidal subunits, which undergo either a fragmentation mechanism, whereby the subunits rotate relative to one another while preserving overall unit orientation, or a reconstitution mechanism in which all subunits rotate as a rigid body. Owing to their kinematic architecture, both metamaterials share common on-axes Poisson's ratios at two critical configurations: (i) in the reconstituted state and (ii) at the instant just prior to fragmentation. Beyond this point, under finite rotation of the subunits, the two on-axes Poisson's ratios bifurcate. These conditions correspond to unique geometric configurations that delimit the transition between common and bifurcated Poisson's ratios. The resulting metamaterials combine Poisson's ratio sign-switching, discontinuity, constancy under reconstitution, and pseudo-bifurcation under fragmentation-features not simultaneously present in earlier fragmentation-reconstitution (FR) metamaterials.
The reduction of the photoemission signal from the Shockley-type surface state of the Ag(110) surface upon the growth of one-dimensional single stranded Si nanoribbons (NRs) is modeled using a customized Poelsema-Comsa (P-C) geometric scattering model. The P-C model takes into account results from scanning tunneling microscopy data on the lengths of Si NRs, the release of Ag adatoms and the formation of narrow finger-like Ag terraces. The simulations show that the newly formed narrow Ag terraces have a negligible effect on the depopulation of the state, whereas the presence of Ag adatoms dominate the depopulation at higher coverage. We determine a depopulating effect of the Si NRs upon the Ag surface state in terms of a nanoscale patch area over which the Si NRs, and the Ag adatoms that they generate, subtract from the photoemission signal from the surface state. We find that the patch area is equivalent to each Si NR deactivating an orthogonal distance 0.6 nm either side of the NR. The work function of the surface is measured, revealing a linear increase in work function upon increasing Si NR coverage.
Rare-earth titanates RTiO3 exhibit a magnetic crossover from G-type antiferromagnetism (G-AFM) to ferromagnetism (FM) governed by the A-site ionic radius. We investigate the phase-boundary solid solution Gd0.5Sm0.5TiO3 using density functional theory (DFT) + U calculations to analyze competing magnetic orders. Our results identify the G-AFM configuration as the zero-temperature DFT ground state, separated from the metastable FM state by only 13.54 meV/Ti, indicating that 50% Sm substitution drives the system into the AFM regime. Conversely, A-type AFM and C-type AFM configurations are dynamically unstable. Analysis of local magnetic moments reveals robust rare-earth ferrimagnetism but highly sensitive Ti moments (0.15-0.64 ) arising from exchange frustration. The energetic proximity of the G-AFM and FM phases suggests that field-induced metamagnetic transitions are achievable at accessible magnetic fields (5-10 T). Thus, the Gd1 -xSmxTiO3 series offers a tunable platform for optimizing magnetocaloric effects for cryogenic cooling applications.
During bonding and service processes, the remarkable anisotropic behavior of hexagonal Cu6Sn5 (eta-Cu6Sn5) intermetallic compound (IMC) in Sn-based solder/Cu joints may result in abnormal IMC growth and subsequent failure of the solder joints. In this work, the crystalline structure, elastic properties, fracture toughness and electronic features of hexagonal eta-Cu6Sn5 with Co atoms doped at the various unfilled Cu2 sites were systematically analyzed using first-principles methods. The Young's and bulk modulus of the Co-free eta-Cu6Sn5 and its doping systems were characterized by three-dimensional plane projections constructions, and the Young's and shear modulus were characterized by two-dimensional plane projections. The results revealed that doping Co atoms can change the elastic anisotropy and shear resistance of eta-Cu6Sn5. Doping Co into most sites can enhance the fracture toughness of eta-Cu6Sn5 to varying degrees. Electronic structure analyses demonstrated that the doping of Co changed both the electronic configuration and structural stability of eta-Cu6Sn5. Specifically, hybridization between Co-d and Sn-p orbitals was observed, which results in a higher peak intensity near -1.51 eV. Notably, Co-doping at particular sites led to significant improvement in the structural stability of eta-Cu6Sn5.
Using first-principles calculations, we investigate dopant-induced magnetism in hydrogen-passivated black arsenic nanoribbons. Light main-group dopants induce spin splitting and local magnetic moments, while heavy dopants suppress magnetism. Band structure and density of states (DOS) analyses reveal a unified mechanism: the competition between localized and delocalized dopant-induced pz impurity states governs exchange-driven spin polarization. Light dopants form localized states near the Fermi level due to significant orbital energy mismatch with the host, thereby enhancing the DOS and promoting magnetism. In contrast, heavy dopants hybridize strongly with As p orbitals through better energy alignment, which quenches the magnetic moments. This mechanism is robust against edge geometry changes. Spin-dependent transport reflects these magnetic states with edge-dependent characteristics, offering insights into impurity-driven magnetism and its modulation in group-V nanostructures.
We report the results of a survey aimed at assessing how beach sprint coastal rowers perceive their sport in terms of injury likelihood and overall risk, their willingness to use personal protective equipment (PPE) and the factors that discourage PPE adoption. Building on these findings, this study demonstrates how auxetics can be exploited in the design of next-generation PPE for use in this new Olympic discipline. By examining well-known auxetic motifs based on the rotating squares/triangles mechanisms, we explore how that PPE can be engineered to provide improved conformal fit enabling the equipment to adapt dynamically to body contours during movement without imposing significant restrictions on mobility. This and other attributes such as enhanced breathability and visual appeal directly address the factors influencing beach sprint coastal rowers' decisions regarding the use of PPE.
In this work a comprehensive computational investigation of thedeformation mechanism governing auxetic behavior in the three-dimensional covalent organic framework (COF) JUC-530 is presented. 3D COFs are crystalline porous polymers constructed from organic building blocks linked by covalent bonds, resulting in 3D frameworks with permanent porosity and tunable topology. Through molecular modeling studies using consistent-valence force field and polymer consistent force field, the empty framework is shown to exhibit a negative on-axis Poisson's ratio of approximately -0.30 in the (001) plane, arising from a cooperative tetrahedral-flattening mechanism involving nested small and large tetrahedral motifs linked through rigid linkers. Loading the framework with nitrogen, methane, or benzene suppresses this auxetic response, shifting the Poisson's ratio toward less negative values. This suppression originates from guest-induced asymmetry in the deformation of the tetrahedral motifs, together with possible steric and/or pi-pi or CH-pi interactions. The interplay between topology, linker rigidity, and guest-framework interactions shows that the auxetic behavior of JUC-530 is a tunable property sensitive to the chemical environment of the pores.
Auxetic structures exhibit distinctive deformation characteristics that give rise to unconventional mechanical responses, characterized by a negative Poisson's ratio (PR) under deformation. While most designs emphasize auxetic behavior, less attention is directed toward resulting stress distributions. The present study addresses this gap by predicting the PR and stress-concentration characteristics of an S-shaped auxetic structure, which is observed to exhibit lower stress concentration than conventional re-entrant configurations. Two prediction models were developed using machine learning techniques, i.e., regression analysis and an artificial neural network (ANN), based on a full-factorial design of experiments comprising 27 simulations. The regression model produced high coefficients of determination, with R2 values of 99.43% for the PR and 92.91% for the von Mises (VM) stress, along with average percentage errors of 1.9023% and 9.6215%, respectively. The ANN model demonstrated stronger performance, achieving an overall correlation of 0.99962 and average percentage errors of 0.6585% for PR and 3.024611% for VM stress. Statistical evaluation confirmed the goodness-of-fit for both models at the 95% confidence level, indicating no significant differences between finite element modeling (FEM) and predicted responses. Overall, the the ANN model offers superior predictive accuracy, making it an effective alternative to resource-intensive simulations/experiments.
This study examines the quasi-static compressive response of functionally graded auxetic triply periodic minimal surface (AUXTPMS) metamaterials designed to stabilise negative Poisson's ratio behaviour at large strains. The proposed concept combines a re-entrant auxetic deformation mechanism with an in-plane porosity gradient generated through an image-modulated implicit-field workflow and isosurface extraction. Polymer (PA2200) and metal (stainless steel and aluminium) were tested in uniaxial compression, and transverse deformation was quantified using video image analysis complemented by digital image correlation. In contrast to uniform-porosity counterparts that exhibited early localisation and out-of-plane instability, the graded architectures promoted stable, sequential crushing and maintained a negative Poisson's ratio over an extended strain range, with the re-entrant 1 & times; 1 configuration showing the most sustained auxetic response. Mechanical response analysis indicated that porosity gradation did not provide a universal increase in peak strength or stiffness-to-weight ratio, but it consistently improved deformation stability by suppressing out-of-plane buckling. Follow-on testing of the selected 1 & times; 1 design in aluminium and stainless steel demonstrated material-dependent specific energy absorption, reaching 2.63 and 5.05 J/g, respectively. Overall, the results identify porosity gradation as a key stabilisation strategy for practical auxetic TPMS architectures, enabling predictable deformation paths relevant to lightweight energy-absorbing and impact-mitigation applications.
We report the structural, chemical, magnetic, and magnetocaloric properties of Ho3+ substituted La0.67Sr0.33MnO3: stoichiometric La0.6Ho0.07Sr0.33MnO3 (LSMO-Ho) and its Sr-deficient composition, La0.6Ho0.07Sr0.33-yMnO3 (y = 0.07) with approximately 21% deficiency at the Sr-site (LSdMO-Ho). Both compounds were synthesized by the solid-state method, and their phase formation was confirmed by X-ray diffraction and Rietveld refinement, revealing a rhombohedral R-3c structure, with a minor Mn3O4 secondary phase in the Sr-deficient sample. Scanning electron microscopy showed dense microstructures with sub-5 mu m grains, while field-emission scanning electron microscopy and energy-dispersive x-ray spectroscopy with elemental mapping confirmed dense microstructures with uniform elemental distribution, while clearly evidencing the effect of Sr-site deficiency on grain morphology and stoichiometry. X-ray photoelectron spectroscopy analysis of LSMO-Ho revealed the presence of Mn in mixed Mn3+ and Mn4+ oxidation states, whereas LSdMO-Ho demonstrated an interplay involving Mn2+, Mn3+, and Mn4+ induced by Sr site deficiency. X-ray fluorescence spectroscopy verified the stoichiometric variations, with reduced SrO and enhanced La2O3/Ho2O3 fractions in LSdMO-Ho. Magnetic measurements demonstrated that Sr-deficiency reduces the T C bringing it closer to room temperature. The Delta S M values were recorded for both the samples under a 5 T magnetic field, with deficient samples showing slightly lower Delta S M. Sr-site deficiency in Ho-doped LSMO not only shifts T C closer to room temperature but also increases the refrigerant capacity, according to the combined structural, spectroscopic, and magnetic characterizations.
External mechanical loadings can change the bandgap of phononic metamaterials by altering their structure or material properties. However, traditional trampoline metamaterials are typically loaded in one or two dimensions. The potential to adjust the bandgap by loading in three dimensions is still in the early stages. This study proposes a trampoline metamaterial with a negative Poisson's ratio (TM-N), which adjusts the bandgap through small deformations under three-dimensional loading. The dispersion curves of TM-N and TM-P are compared using mass-spring models and finite element (FE) simulations. Compared to TM-N, TM-P shows an opposite trend in the bandgap when the substrate is compressed. The adjustable performance of the TM-N bandgap under prestress is also discussed. Numerical results show that increasing the strain ratio chi expands the bandgap and increases its bandwidth. The effects of cylinder perforated ellipticity and substrate thickness T on the bandgap are analyzed. With chi = -2, = 4, and T = 5.5 mm, the minimum starting frequency of the bandgap is 134.5 Hz, and the relative bandwidth is 86%. The proposed TM-N effectively reduces the bandgap frequency and widens the bandgap range under three-dimensional loading, offering new possibilities for real-time bandgap adjustment.
Element doping stabilizes SmFe12-based magnets but typically reduces saturation magnetization. To elucidate the underlying mechanisms, this study employs first-principles calculations to analyze the site preference of eight dopants (Ti, V, Ga, Al, Si, Nb, Mo, Co). Results indicate that Ti, V, Nb, and Mo prefer the 8i site, while Al, Ga, and Si occupy the 8j site. The total magnetic moment is primarily determined by three factors: (1) Site-specific Fe moments, following the order mu(8f) < mu(8j) < mu(8i), where 8i-substitution causes the largest moment loss; (2) the intrinsic magnetism of doping elements, which, based on density of states (DOS) analysis, are classified into a negative contribution group with moments anti-parallel to Fe (Ti, V, Nb, Mo), a non-magnetic group (Al, Ga, Si), and a positive contribution group (Co); and (3) the influence of doping elements on surrounding Fe moments, where Co, Ga, and Al significantly enhance the total magnetic moment of surrounding non-substituted Fe atoms. This work provides a quantitative framework for screening magnet candidates specifically from the perspective of optimizing saturation magnetization and site-occupation trends.
We report the crystal structure, elasticity, phonon spectrum, electronic structure and ferroelectricity of KMgSb in the wurtzite LiGaGe-type phase. The simulation is performed by means of total-energy calculations within density-functional theory (DFT). The mechanical and dynamical stability of the material studied are verified via the elastic constants and phonon frequencies. The electronic structure is described in terms of the band structure and density of states. In order to overcome the inherent shortcoming of DFT in reproducing bandgaps, the local-density approximation is used in combination with the modified Becke-Johnson functional. It is shown that wurtzite KMgSb exhibits an indirect bandgap of 1.54 eV and low effective masses around +/- 0.5. We also employ the Berry-phase theory to provide the spontaneous polarization and Born effective charges associated with the polar wurtzite structure of KMgSb. The spontaneous polarization is found to be equal to 0.37 C/m2, and the effective charges are close to their nominal values. Furthermore, we demonstrate the ferroelectric behaviour by computing the double potential well that characterizes polarization switching. The low values of the switching energy barrier (0.093 eV/f.u.) and coercive electric field (7.31 MV/cm) suggest that the polarization can be reversed quite easily, making wurtzite KMgSb suitable for ferroelectric applications.
In this paper, based on the principle of local resonance, several new three-dimensional labyrinth-type acoustic metamaterials are proposed, and two optimization methods are used to optimize the structures and screen out two structures with excellent performances, that is, model C and model D. Based on Bloch's theorem and the lattice theory, finite-element simulations are performed on different structural elements to analyze the bandgap properties of the structures. The frequency response spectra were subsequently obtained by analyzing the transmission characteristics of the finite periodic structures. The results show that both novel metamaterial structures have good bandgap characteristics, with the widest width of the first bandgap reaching 1197.2 Hz in the low-frequency band 0-2000 Hz, the bandgap coverage reaching 59.9%, and the lowest attenuation peak reaching -256.6, and the structures have excellent vibration and noise reduction capabilities.
The response to non-infinitesimal deformations applied at the innermost level of self-similarity has been studied in star-like hinged gratings showing a 2D chirality implied by the 2D point group 4 (C4) instead of the achiral point group 4 m (D4) known from previous works. The symmetry lowering turns out to impose geometric restrictions on the existence (feasibility) of such twisted stars as well as on the closeability (full foldability) of their central square orifice. The ranges of feasibility and full foldability have been found as functions of the system's parameters, that is the scaling factor and the twist angle. The minimal angle to which a twisted star can be folded when it is not fully foldable has been determined. For some sets of the parameters, the stars turn out fully rigid, that is not foldable at all if the number of self-similar generations tends to infinity. When subjected to even large deformations of their central orifice, the twisted stars recover their generic self-similarity and the four-fold point symmetry at their periphery but the rate of this recovery depends on the twist angle. The results may be useful in the design of nanometric and macroscopic systems based on metamaterials.
The high-pressure structural, mechanical, electronic, and thermal transport properties of the layered MAB-phase ternary boride Hf2SeB are systematically investigated via first-principles across a pressure range of 0-50 GPa. Hf2SeB crystallizes in a hexagonal P63/mmc structure and retains thermodynamic, mechanical, and dynamical stability throughout the investigated pressure regime. Hydrostatic compression induces pronounced anisotropic lattice contraction, with enhanced stiffness along the basal plane relative to the c-axis, accompanied by a pressure-amplified elastic anisotropy. Electronic structure analyses reveal robust metallic conductivity dominated by Hf-d states near the Fermi level, with a substantial pressure-induced increase in the electronic density of states. Notably, compression markedly strengthens the mechanical response, with the theoretical Vickers hardness increasing from 12.02 GPa at ambient conditions to 17.52 GPa at high pressure. In parallel, Hf2SeB exhibits an ultralow minimum thermal conductivity (0.68-0.90 W m-1 K-1) and a continuously rising melting temperature, suggesting its potential for applications in high-pressure, high-temperature, and thermomechanically demanding environments, though its oxidation resistance at elevated temperatures remains a critical consideration for practical use.
We investigate the impact of electronic correlation effects on diode efficiency in a quantum dot Josephson junction that contains a single magnetic impurity. This study employs the exact diagonalization method within the framework of the zero bandwidth approximation. By adjusting system parameters such as the coupling strength between the quantum dot and the impurity, the intra-dot Coulomb interaction strength, we examine how these factors affect the Josephson current, spin correlation functions, and the efficiency of Josephson diodes. We find that various electronic correlation effects exist in the system. When the system parameters change, these electronic correlation effects can exhibit phenomena of both competition and cooperation. This not only leads to the emergence of - Josephson phase transitions but also alters both the magnitude and sign of the diode efficiency in the system. Our research findings indicate that these intriguing physical mechanisms profoundly influence properties such as current magnitude and efficiency in Josephson diodes.
The different atomic percentages of Fe and Ti during the solidification process and their influence on the local atomic structure of ferrotitanium alloys have been investigated using molecular dynamics simulations. To examine the material's atomic characteristics, we perform the calculation of the radial distribution function (RDF) and structure factor S(q) at 300 K. The results show that variations in atomic composition lead to differences in the formation of local structures. The body-centered cubic structure becomes increasingly prominent when the Fe content is higher than the Ti content. In contrast, the hexagonal close-packed structure decreases in occurrence as the Fe composition increases. Furthermore, the RDF obtained in this study shows that increasing Fe content leads to a decrease in the positions of the first, second, and third peaks, indicating changes in the local atomic density. In contrast, the structure factor S(q) exhibits the opposite trend, where a higher Fe atomic percentage relative to Ti results in larger first, second, and third peak positions.
This study reveals a concentration-dependent adsorption where alkali ions Lithium (Li), sodium (Na), and potassium (K) preferentially occupy hollow sites at all concentrations. Their adsorption behaviour on armchair graphene nanoribbons (AGNRs) is systematically studied using density functional theory at concentrations of 2.7%, 5.2%, 7.6%, and 10%. Performance is analysed in terms of electronic structure (band structure and density of states), bond lengths (Li-C, Na-C, and K-C), cohesive energy, adsorption energy, open-circuit voltage (OCV), theoretical capacity and diffusion barriers. The results show increasing structural deformation with higher ion concentration. Li exhibits strong chemisorption at all concentrations while Na shows predominantly physisorption due to weaker interaction with AGNR electronic states. K mostly depicts chemisorption but induces significant lattice distortion due to its larger size. Li has the highest adsorption energy whereas Na shows lower adsorption than K due to less effective orbital interaction. All ions exhibit low diffusion barriers (<0.5 eV) indicating good mobility with Li giving highest barrier while K shows the lowest barrier and Na little higher than K. OCV calculations suggest suitability of all ions for anodes in battery applications. The study aims to provide new insights into adsorption limits in AGNRs.
