The transformation from one amorphous phase to another is known as the glass-to-glass transition, which induces significant changes in the structure and properties of metallic glasses. However, the influence of this transition on the β relaxation behavior remains to be clarified. Here, based on classical molecular dynamics simulations of the Zr65Al7Fe7Co7Ni7Ag7 pseudo-high entropy alloy, we find that the as-cast sample (gA) undergoes a glass-to-glass transition upon heating at around 849 K. After isothermal annealing at 900 K, gA transforms into a new metallic glass (gB), and gB does not undergo a glass-to-glass transition upon heating. Compared to gA, gB exhibits a higher probability of Al-Al and Al-Ag bonding and a lower probability of bonding between Al and other atoms. Furthermore, gB also exhibits a more pronounced β relaxation peak and a higher characteristic temperature of β relaxation (Tβ) on the E″/E″max - T/Tα curve. By comparing the atomic mobility in gA and gB at their respective Tβ, we further demonstrate that gB contains a larger number of fast-moving atoms. This higher mobility makes a significant contribution to the more pronounced β relaxation peak observed in gB. Our findings provide a fresh perspective for utilizing the glass-to-glass transition to tune the β relaxation in metallic glasses.

Atomic mobilities and kinetic characteristics in the fcc phase of the Ni-Fe-Si system

HighlightsMD simulations reveal CSH/SiO2 interface degradation under heat–water coupling.Thermal excitation enhances atomic mobility, disrupting Ca-O bond and H-bond networks.High temperature induces ITZ expansion and structural loosening of the interface.Water competes for active sites, turning direct CSH/SiO2 bonding into water-mediated.High temperature acts as a catalyst for deeper water molecule penetration into CSH.As the critical weak link in grouting reinforcement systems, the interfacial adhesion between cementitious grout and rock minerals is highly susceptible to performance degradation under high-temperature and water-rich conditions. In this paper, molecular dynamics simulations were performed across a temperature range of 293 K to 368 K to systematically investigate the effects of high-temperature and water-rich environments on the mechanical response, bonding structure, and dynamic behavior of the grout–rock interface. All simulations were performed using the LAMMPS package with the ClayFF force field. Two interface models, including a CSH/SiO2 direct-contact model and a CSH/H2O/SiO2 water-containing model, were constructed and subjected to uniaxial tensile tests. Key findings are as follows: (i) The tensile strength and interaction energy of the CSH/SiO2 interface exhibit distinct thermal degradation characteristics. The tensile strength decreases by 32.57%, and the interaction energy by 15.78% when the temperature rises from 293 K to 368 K. High temperatures induce expansion of the interface transition zone from 2.74 Å to 4.60 Å and loosening of the interface structure. (ii) High temperatures intensify atomic diffusion at the interface. The number and stability of Ca-O bonds and hydrogen bonds formed between CSH and SiO2 are reduced, leading to a decline in interfacial adhesion. (iii) The presence of an interfacial water layer significantly impairs the tensile strength and interaction energy of the interface. Compared with the direct-contact interface, the interaction energy is reduced by 38% at 293 K, and the tensile strength decreases by 73.58%. Water molecules in the solution compete for bonding sites of hydrogen bonds and Ca-O bonds at the interface, weakening the direct interaction between CSH and SiO2 and transforming it into an indirect interaction mediated by water molecules.

Molecular dynamics simulations were performed to investigate the nanometric cutting of polycrystalline oxygen-free copper using a single-crystal diamond tool. The effects of grain size, tool geometry (rake angle and edge radius), cutting speed, and ambient temperature on atomic migration, dislocation activity, and tool wear were systematically analyzed. The results indicate that material removal is dominated by cutting-induced amorphization and the formation of hcp-coordinated defect structures, while dislocation activity governs plastic deformation and cutting force fluctuations. A damaged subsurface layer, composed of amorphous structures, hcp-coordinated defects, and residual dislocations, is formed beneath the machined surface. Increasing grain size reduces grain-boundary-induced stress concentration and suppresses subsurface damage. A larger rake angle facilitates chip removal and reduces damage, whereas a larger edge radius intensifies dislocation activity and amorphization. Higher cutting speeds reduce lattice distortion and subsurface damage but increase stress concentration on the tool. Elevated temperature enhances atomic mobility, promoting amorphization and subsurface deformation while accelerating tool wear. These findings provide insight into the nanometric cutting behavior of polycrystalline copper and offer guidance for optimizing process parameters to improve surface integrity and tool life.

Machine learning surrogates for CALPHAD inputs in mean-field precipitation modelling of IN738LC

High-entropy alloys (HEAs) are promising candidates for advanced nuclear structural materials, owing to their superior mechanical properties and irradiation resistance under extreme service conditions. However, microcracks generated during fabrication and service significantly limit their operational lifespan. The evolution of chemical short-range order (SRO) under irradiation exerts a pivotal regulatory effect on the crack self-healing behavior of HEAs. In this study, molecular dynamics simulations were systematically performed to elucidate the regulatory mechanism of SRO on crack healing behavior in NiCoCrFeMn HEAs under ion-induced cascade collisions. The results reveal that an optimal SRO degree induced by 600 K annealing achieves a balanced trade-off between point defect density and atomic mobility. This leads to complete crack closure with 100% healing efficiency, significantly outperforming the random solid solution (RSS) and other degree of SRO models. Specifically, SRO guides the selective segregation, enrichment, and filling of Co, Fe, and other elements in the crack region, while promoting the formation of a dense, entangled three-dimensional dislocation network dominated by 1/6<112> Shockley partial dislocations and 1/6<110> stair-rod dislocations. Additionally, irradiation-induced amorphous regions undergo recrystallization into stable FCC/HCP phases, further facilitating crack self-healing and ensuring long-term structural integrity under irradiation. Collectively, SRO governs the crack self-healing process in NiCoCrFeMn HEAs by synergistically modulating defect evolution, atomic migration, dislocation dynamics, and phase transformation. This work overcomes the inherent limitations of conventional RSS-based HEA designs and offers critical theoretical insights and guidance for the precise SRO engineering of next-generation irradiation-tolerant and self-healing nuclear structural materials.

Diffusivity and atomic mobility assessment in U-X (X = Nb/Mo) liquids: integration of AIMD simulations and CALPHAD modeling

ABSTRACT Room‐temperature epitaxial growth of functional oxides on wide‐bandgap semiconductors is critical for heterogeneous integration and functional diversification, yet remains largely unachieved due to insufficient atomic mobility and severe lattice/chemical mismatch. Here, we introduce a reactive‐template‐induced strategy (RTIS) that enables atomically precise NiO/4H‐SiC heterostructures via room‐temperature pulsed laser deposition (PLD). Face‐selective epitaxy on Si‐terminated versus C‐terminated surfaces confirms a chemical−template mechanism mediated by Si−O−Ni bonding. The undoped NiO films exhibit exceptional crystallinity with crystal tilting of only 82 arcseconds and atomically sharp interfaces. Li‐doping preserves the epitaxial quality, enabling dual‐mode ultraviolet (UV) photodetectors based on oxide/semiconductor heterostructures with both solid‐state and photoelectrochemical (PEC) operation. The solid‐state device demonstrates impressive performance with a responsivity of 2.09 A W −1 and detectivity of 1.09 × 10 14 Jones under 254 nm illumination. The PEC‐mode device achieves a responsivity of 159 mA W −1 , sub‐millisecond response times, and remarkable longterm operational stability even in natural seawater. First‐principles calculations reveal fundamentally distinct interfacial electronic structures at NiO/metal versus NiO/liquid junctions, elucidating the underlying mechanisms responsible for their contrasting operational behaviors. RTIS extends to multiple wide‐bandgap platforms (GaN, AlGaN, ε‐Ga 2 O 3 , 3C‐SiC), establishing a versatile pathway for oxide/WBG integration with implications for advanced optoelectronic and (photo)electrocatalytic systems.

Silver-coated copper (Cu@Ag) core-shell nanoparticles are promising interconnect materials for electronic packaging due to their high conductivity, oxidation resistance, and reduced use of precious metals. However, the key factors governing their sintering behavior and mechanical performance are not fully understood. In this study, molecular dynamics simulations were performed to examine the effects of sintering pressure (300-700 MPa), temperature (500-700 K), particle size, and silver shell thickness on atomic diffusion, microstructural evolution, and mechanical properties. Results show that higher pressure improves particle contact, accelerates densification, and strengthens interfacial bonding, with optimal performance achieved at 600-700 MPa. Elevated temperatures enhance atomic mobility, promoting neck growth and pore elimination, with the most active diffusion observed between 650 K and 700 K. Particle size and shell thickness also affect sintering: the Ag6Cu3 configuration exhibits the highest atomic mobility and a balanced combination of strength and ductility. Moderately thick silver shells facilitate surface diffusion and interfacial interdiffusion, while mechanisms such as the Kirkendall effect and local plastic relaxation reduce defect density, yielding stable sintered structures. These findings provide atomic-scale insights into the sintering mechanisms of Cu@Ag nanoparticle solder pastes and offer guidance for optimizing processing parameters in high-performance electronic packaging applications.

ABSTRACTRotation of crystal seed during the early stages of growth around 3000K in a glass matrix has been observed due to some torque, contradicting the expectations from the isotropic, uniform structure of the surrounding amorphous matrix. We establish an atomistic origin of this new phenomenon from molecular dynamics simulations using LiNbO3 and LiNbO3‐SiO2 glasses as model systems. Effectively, it arises due to non‐uniform forces on the seed from the surrounding glass, which appears inhomogeneous and anisotropic on the scale of glass‐crystal interface. The seeded crystal growth (SCG) at higher temperatures amplifies this effect due to enhanced atomic dynamics. Silica, when added to LiNbO3 glass, reduces the crystal growth rate due to increased viscosity and restricted atomic mobility across the growth interface, but has minimal effect on the crystal rotation. These findings challenge a general assumption that glass is an isotropic material, especially during the early stage of its crystallization, and provide insights for tailoring the microstructure of widely used glass‐ceramics.

Abstract Calcium fluoride (CaF2 ) is a key functional material for next-generation lithography; however, limited understanding of its microscopic nucleation and growth mechanisms has led to continued reliance on empirical parameters during synthesis. To address this, we employ&amp;#xD;molecular dynamics (MD) simulations using a neuroevolution potential (NEP) trained on ab initio molecular dynamics (AIMD) data to investigate CaF2 crystallization, and analyze key kinetic and thermodynamic properties including species-resolved self-diffusion&amp;#xD;coefficients (DCa and DF ) and thermal conductivity. Based on these results, we show that&amp;#xD;temperature oscillation facilitates CaF2 crystallization and identify an effective temperature window of 800–1400 K (Tm = 1715.72 K), within which moderate atomic mobility and stable heat transport jointly promote abnormal grain growth (AGG). We further ob-&amp;#xD;serve interface-induced growth and clarify anisotropic growth across the (100), (110), and (111) planes, with the (110) plane exhibiting faster growth at 1100 K, and propose an approximate method for evaluating growth rates. This work provides mechanistic insights&amp;#xD;into CaF2 crystallization and offers guidance for optimizing the synthesis of high-quality CaF2 .

Abstract The inner core (IC) of Earth, the central part of our planet, was formed and grew because of the solidification of liquid iron (Fe) alloys in the outer core. To understand how hexagonal close-packed iron (hcp-Fe) behaves under extreme conditions, it is crucial for interpreting the seismic data and modelling how the Earth’s IC evolves over time. In this investigation, we tried to explore the mechanical behaviour of hcp-Fe in an IC-like environment using advanced computational methods by combining strategic density functional theory (DFT) in conjunction with molecular dynamics (MD) simulations. This approach allowed us to explore the structural and mechanical properties of hcp-Fe in the unique combination of pressure and temperature found in the IC. Our results reveal significantly higher tension, compressive, and shear strength of iron in IC conditions as compared to the ambient pressure and temperature conditions. In addition, we explored the effect of different crystal orientations on the compressive and tensile strength of hcp-Fe under IC conditions. The diffusion rate difference in different crystal arrangements significantly affects hcp-Fe's compressive and tensile strength under extreme conditions. Low diffusion rate corresponds to lower atomic mobility, which results in higher mechanical strength in the [0001] orientation and development of the basal slip system under dislocation creep. In addition, the reduction in dislocation density at 6000 K in each orientation indicates a complex rheology mechanism under IC conditions. This study is crucial to understanding the mechanism of anisotropic behaviour and diffusion-dynamics within Earth’s IC.

In recent years, the demand for ultrasonic vibration-assisted forming has been increasing because of its energy efficiency and high precision. The acoustic softening effect induced by ultrasonic loading reduces flow stress and promotes metal softening. However, the underlying microstructural mechanisms remain unclear. This study investigates the mechanism of acoustic energy absorption by dislocations in body-centered cubic (BCC) iron. The kinetic states of atoms surrounding an edge and a screw dislocation under ultrasonic excitation are analyzed using molecular dynamics simulations. The results demonstrate that atoms around edge dislocations absorb ultrasonic energy more efficiently than those in a perfect crystal. This is because the reduced atomic density along the slip direction enhances atomic mobility. In contrast, screw dislocations, whose interatomic spacing along the slip direction remains uniform, absorb energy through a different mechanism: local lattice distortion reduces the interatomic spacing perpendicular to the slip plane, enhancing atomic mobility along the slip direction under vibration. Under ultrasonic loading, both edge and screw dislocations reduce yield stress by 47.0% and 15.9%, respectively, consistent with their preferential acoustic energy absorption mechanisms. Furthermore, the combination of the shear strain components and applied ultrasonic vibration significantly influences the degree of stress reduction, depending on how the vibration couples with the slip direction of the dislocation. These findings provide atomistic insights into the interaction between BCC dislocations and ultrasonic vibrations and clarify the origin of ultrasonic-induced softening in metals.

Diffusion-controlled processes exert an indispensable influence on the thermal processing and microstructural homogenization of β-titanium alloys containing multiple β-stabilizing elements. However, credible multicomponent diffusion kinetic data corresponding to the β-phase within the Ti-Zr-Ta ternary system remain inadequate. In this work, diffusion characteristics within the β single-phase domain of the Ti-Zr-Ta system were investigated using solid-state diffusion couples combined with a numerical inverse method. Twelve diffusion couples in total were synthesized and subjected to annealing treatments at 1373, 1423, and 1473 K, with the corresponding composition-distance distributions quantified by electron probe microanalysis (EPMA). The composition-dependent main interdiffusion coefficients were measured via the numerical inverse method embedded in the HitDIC computational platform, while the atomic mobility parameters corresponding to the β-phase were refined to replicate the experimental concentration distributions and diffusion trajectories across the studied temperature and composition intervals. The results reveal pronounced temperature and composition dependence of the main interdiffusion coefficients, and the diffusion rate of Zr is faster than that of Ta in the β phase.

The reactions of oxygen (O2) and water (H2O) molecules with metal surfaces are critical to heterogeneous catalysis, corrosion, and electrochemical energy conversion. However, disentangling their individual roles remains challenging because both pathways yield the same dissociation product, atomic oxygen (O), and share the hydroxyl (OH) intermediate, thereby obscuring the molecular origin of metal oxidation. In this study, we combine in-situ transmission electron microscopy techniques and ReaxFF reactive force field molecular dynamics (MD) simulations to elucidate the promotional role of H2O in copper (Cu) surface oxidation. Our results reveal that the structurally disordered Cu/CuOx interface preferentially adsorbs OH derived from H2O dissociation. The resulting strong Cu-OH interaction causes dynamic disorder in the topmost Cu layer while enriching electron density in the sublayer. This coupled structural and electronic modulation lowers the resistance for oxygen incorporation, promoting deeper lattice penetration, accelerating oxidation, and enhancing Cu atomic mobility. In contrast, oxidation under pure O2 produces a comparatively ordered interface that suppresses sustained oxygen ingress, rendering further oxidation kinetically less favorable. These findings identify OH-mediated interfacial dynamics as a key driver of water-assisted metal oxidation and provide mechanistic guidance for controlling oxidation processes in catalytic and corrosion-resistant materials.

Photonic-crystal surface-emitting lasers (PCSELs) are a new type of semiconductor laser with the potential for high-power output and high-beam-quality operation. Integrating a distributed Bragg reflector (DBR) into PCSELs can significantly enhance device performance. However, the growth of high-aluminum-content DBRs on photonic crystal layers with buried air holes presents two major challenges. First, the low mobility of aluminum atoms increases the propagation of surface roughness from the substrate into the DBR, increasing defect density. Second, the high growth temperatures required for DBR growth can deform the thermally unstable air holes. In this work, we investigated a metal–organic chemical vapor deposition (MOCVD) regrowth process for fabricating DBRs on PCSELs. By adjusting the epitaxial growth temperature and V/III ratio, we effectively controlled the diffusion of adatoms on both the sample surface and inside the holes. As a result, the root mean square (RMS) surface roughness decreased by ~96%, and uniform buried air holes were obtained, with a filling factor of ~ 18.8% and a depth of ~ 270 nm, without significant deformation. Finally, we fabricated a PCSEL device with a DBR structure, exhibiting a beam divergence angle of ~ 0.5° and a peak power of about 0.86 W. This study provides a key process solution for the development of PCSELs with high-quality DBR structures, enabling further improvement in optical output performance.

Diffusivities and atomic mobilities of fcc phase in Co-rich Co–Fe–Ti system: Experimental study and CALPHAD assessment

HCN channels have a reverse electromechanical coupling mechanism, where hyperpolarized membrane potentials facilitate pore opening through an inward displacement of the S4 segment of the voltage-sensing domain (VSD). This voltage dependence is finely regulated by the binding of cAMP to an intracellular domain (CNBD). Of the four widely studied isoforms of human HCN channels, the HCN3 channel is practically insensitive to cAMP or is even inhibited by it, but the structural determinants underlying this unexpected behavior are still unclear. Here, we evaluated the possible role of flexibility in very specific regions of the VSD that could be determinants for this behavior. Part of the S2-S3L linker is more rigid in HCN3, which correlates with low atomic mobility for this region in proximity to the C-linker subdomain of the opposite subunit. We built structural models using AlphaFold 3 and Swiss-Model and thus reconstructed the disordered regions that connect the transmembrane segments of the VSD and that in some of the structures deposited in the PDB have not been resolved. Besides, in an attempt to reveal the evolutionary trends that this transmembrane domain may have undergone, we conducted a comparative study with phylogenetically distant HCN channels and found an interesting tendency to lose sensitivity to cAMP as VSD flexibility is lost. Our analysis confirms a large body of published experimental findings. Finally, we found that in metazoans, two types of HCN channels clearly diverge: (1) those that are highly sensitive to cAMP with moderate flexibility profiles in protostomes, and (2) those that show less marked sensitivity to this ligand in deuterostomes. We also propose a possible evolutionary scenario for the appearance of cAMP-modulated HCN channels in the last eukaryotic common ancestor (LECA).

This study evaluates the effects of sintering time and applied pressure on the microstructure and Vickers microhardness of the CoCrFeMnNiAl1.5 alloy during consolidation. Samples were obtained by mechanical alloying and consolidated using two routes: conventional sintering (CS) and high-frequency induction sintering followed by high-temperature heating (HFIHS + HTH). For both methods, the pressure (0.3–1.5 GPa) and holding time (1–4 h) were varied. The results show that the HFIHS + HTS route produces a finer microstructure, with notably more homogeneous Cr segregation at high pressures, resulting in higher Vickers hardness values (up to 770 HV). In addition, the pressure applied during HFIHS promotes a mechanism of forced atomic mobility. This mechanism facilitates the migration of atoms toward energetically favorable sites, such as grain boundaries. At the same time, it restricts precipitate growth and Cr-rich segregation and activates densification mechanisms without requiring sustained pressure. The optimal parameters (0.9 GPa and 1 h) produce the best microstructural and mechanical response, highlighting the potential of this alloy for use in coatings and structural components in the automotive and aerospace industries.

ABSTRACT Silicon carbide (SiC) is widely employed as a friction-pair material in high-load and extreme-service environments due to its superior wear resistance and high-temperature stability. However, continuum-based tribological models have limited capability in capturing interfacial deformation and material removal mechanisms at the atomic scale. In this work, molecular dynamics simulations were performed using LAMMPS and analysed/visualised with OVITO to investigate how temperature (300, 700, and 1100 K), penetration depth (10, 12, and 14 Å), and sliding velocity (0.2, 0.5, and 0.8 Å/ps) influence the tribological response of SiC. The results indicate that increasing temperature generally reduces both friction and normal forces, consistent with thermal softening and enhanced atomic mobility, while the friction coefficient shows only a weak and slightly non-monotonic dependence across the studied range. Penetration depth plays a dominant role: deeper indentation markedly increases tangential resistance and the friction coefficient, which is associated with an expanded plastic deformation zone and a thicker third-body debris layer. By contrast, under a fixed penetration depth of 10 Å, the average friction coefficient is largely insensitive to sliding velocity within 0.2–0.8 Å/ps, although higher velocity intensifies force fluctuations. These findings provide atomic-scale insights into the governing mechanisms of SiC friction and wear and offer guidance for performance optimisation under extreme operating conditions.