Analysis Of Coordination Numbers Research Articles

Bridging molecular dynamics and additive manufacturing: A study of Al-12 at% Si alloy solidification dynamics

This manuscript provides a detailed analysis of the molecular dynamics of the directional solidification process in Aluminum-Silicon (Al-12 % at Si) alloys, with a particular emphasis on applications in additive manufacturing. Utilizing molecular dynamics (MD) simulations, the study examines large systems containing 5–15 million atoms to investigate various facets of the solidification process. These include the dynamics of interface motion and the formation of Silicon (Si) precipitates. The research reveals significant variations in interface velocities and orientations across different thermal gradients and growth rates, underscoring the intricate interaction between thermal and solute flows in the microstructural development of Al-Si alloys. These findings are vital for comprehending and refining the solidification process in additive manufacturing, ultimately enhancing the mechanical strength and reliability of the final products. The paper highlights the critical role of microstructure control in printed metals and proposes future research directions, aiming to apply these insights to more complex alloy compositions and manufacturing contexts. In the concluding phase, the scikit-image library was employed to analyze dendritic formations in solidifying Al-Si alloys using MD simulations. This analysis delineates trends in dendritic count, spacing, perimeter, and area over time, offering essential perspectives on the solidification process and its implications for the alloy's microstructure and mechanical characteristics. The Si content in the Al-Si alloy used can be considered eutectic in the solidified structure. Si atoms are predominantly located at grain boundaries and precipitate regions. Coordination number analysis further confirms the presence of Si in these locations. This microstructure, characterized by a primary Al/Al-Si matrix and Si-rich eutectic regions, aligns with experimental observations in rapid solidification processes in additive manufacturing.

Unveiling the dissolution behavior of letrozole in fourteen pure solvents: Insights from experiments and molecular simulations

The dissolution behavior of an active pharmaceutical ingredient (API) in different solvents is of great importance for the design and optimization of its crystallization process. In this study, the solubility of letrozole in fourteen pure solvents was determined using a gravimetric method within the temperature range of 283.15–323.15 K at atmospheric pressure. The results demonstrate a significant correlation between letrozole’s dissolution behavior and the molecular structure (carbon chain length and presence of branched chains) and properties (dielectric constant and cohesive energy density) of the solvent. Solubility analysis and simple crystallization experiments suggest that acetonitrile may serve as a suitable solvent for the cooling crystallization of letrozole. To enhance the applicability of solubility data, five mathematical models were employed for data fitting. In addition, the Van’t Hoff equation was utilized to calculate the apparent thermodynamic properties of the letrozole dissolution process. Furthermore, molecular simulations were conducted to investigate the dissolution behavior of letrozole in different solvents, revealing distinct patterns of interaction between solute and solvent molecules. Specifically, in alcohol solvents, alcohol ether solvents, and acetonitrile, solute molecules interact with solvent molecules primarily as hydrogen bond acceptors, whereas the opposite behavior is observed in ester solvents and acetone. Binding energy, radial distribution function (RDF), and coordination number (CN) analyses effectively elucidate the dissolution behavior of letrozole in solvents of the same category, indicating that stronger solute–solvent interactions result in higher solubility. A comprehensive examination of solute–solvent and solvent–solvent interactions offers a rational explanation for letrozole’s dissolution behavior in solvents of different categories, highlighting the decisive impact of solvent–solvent interactions, particularly in alcohol solvents and acetone.

Performance and limits of a geotechnical centrifuge: DEM-LBM simulations of saturated granular column collapse

This study investigates the dynamics of granular flows in geotechnical centrifuge models, focusing on the effects of centrifugal and Coriolis accelerations. While conventional laboratory-scale investigations often rely on Froude scaling, geotechnical centrifuge modelling offers a unique advantage in incorporating stress-dependent processes that fundamentally shape flow rheology and dynamics. Using the Discrete Element Method (DEM) and the Lattice-Boltzmann Method (LBM), we simulate the collapse of a just-saturated granular column within a rotating reference frame. The model’s accuracy is validated against expected trends and physical experiments, demonstrating its strong performance in replicating idealised collapse behaviour. Acceleration effects on both macro- and grain-scale dynamics are examined through phase front and coordination number analysis, providing insight on how centrifugal and Coriolis accelerations influence flow structure and mobility. This work enhances our understanding of granular flow dynamics in geotechnical centrifuge models by introducing an interstitial pore fluid and considering multiple factors that influence flow behaviour over a wide parameter space.Graphical abstract

Investigating medium range order in Mg-Al binary metallic glasses: Molecular dynamics approach

In this work, we used molecular dynamics (MD) simulations in order to investigate the Medium-Range Order (MRO) in Mg-Al binary metallic glasses (MGs). The embedded atom method (EAM) has been adopted to accurately model the interatomic interactions. Various techniques such as radial distribution function (RDF), coordination number (CN) analyses and Gaussian fitting have been mobilized to comprehensively study the impact of cooling rate, composition and mechanical solicitations, on the structural properties at the MRO level. Our results reveal that the 1-atom connection mode is consistently dominant across all cooling rates. Moreover, as the cooling rate increases in the Mg25Al75 binary MG, the abundance of the 4-atom and 2-atom connection modes increases, while the percentage of the 3-atom mode experiences a slight decrease. Furthermore, we investigate the influence of composition on the properties of MgxAl100-x alloys, demonstrating that the RDF peaks and connection modes are highly sensitive to variations in the Al concentration. Additionally, we explore the relationship between mechanical properties and connection modes during tensile deformation. The 3-atom connection mode exhibits superior hardness and stability, while the 4-atom and 2-atom connection modes offer increased flexibility. These significant findings enhance our understanding of MGs structural evolution, stability and deformation behavior. Ultimately, this knowledge facilitates the design and optimization of tailored MGs for advanced applications.

MD Simulation and Transport Property Analysis of Silicon in High-Temperature Molten Fluoride Salts Electrolyte

Silicon is the dominant solar material because of its abundance, low cost, and high solar efficiency. But manufacturing high-purity silicon required for solar energy is very complex, hard to scale, and unsafe since it involves dealing with toxic flammable gases. Therefore, a new solar silicon production technology based on molten salt electrolysis has been proposed. To comprehensively study the self-diffusion and deposition mechanism of silicon ions in high-temperature molten salt electrolyte and their composition and temperature dependence, both interatomic potential molecular dynamics (IPMD) and ab-initio molecular dynamics (AIMD) are introduced. Thermodynamics and transport properties of molten salt electrolyte such as density, heat capacity, viscosity etc. are investigated and compared to the existed experimental results. Also, local structural information and coordination number analysis are obtained and discussed.

Operando X-Ray Absorption Spectroscopy of Pt Catalyst in Polymer Electrolyte Fuel Cell Under High Temperature and Low Humidification

For the widespread use of fuel cell vehicles, it is necessary to improve the performance and durability of the cathode catalyst of polymer electrolyte fuel cells (PEFCs). In particular, high-temperature operation of PEFCs is attracting attention for application to commercial vehicles for heavy-duty application. Operation at higher temperatures than the conventional one (60-80°C) is expected to enhance oxygen reduction kinetics and mass transfer and reduce specific adsorption of ionomers. Despite such advantages, due to the thermal effect, the oxide formation on Pt surface is expected to be enhanced and decrease the activity of the catalyst. However, the quantitative relationship between catalyst behavior and the electronic structure of Pt under high temperature operation has not yet been elucidated. Here, we developed an MEA cell for high temperature and high pressure conditions and analyzed the oxidation state and local structure of Pt on Pt/C catalysts at different temperatures by operando XAS measurements.MEAs were prepared with Pd/C as anode catalyst, Pt/C as cathode catalyst. XAS measurements of the Pt LIII absorption edge were made at 80°C, 105°C, and 120°C with 100% H2 flowing to the anode and Air flowing to the cathode, and spectra were collected by the transmission mode. The area values of the XANES spectra were calculated to compare the relationship of Pt oxide formation with operating temperature and the local structural model of Pt oxide at high temperature by EXAFS.Comparison of operando XANES results of cathode catalyst Pt/C under conventional operating temperature (80°C), 105°C, and 120°C showed a marked difference, especially at 80°C and 120°C. In addition, the XANES area values increased as the operating temperature was increased. This is thought to be due to the fact that Pt oxide formation is accelerated at higher temperatures. Next, comparing the EXAFS analysis results at each temperature, the Pt-O bond peak is stronger at 120°C, indicating that Pt oxidation is more advanced than at 80°C. The 120°C results can be explained by a mixed model of β-PtO2 and Pt metal. Pt-O bond coordination number analysis shows that β-PtO2, in which oxygen is latent inside Pt, is formed more frequently at high temperatures. From this result, it was found that the structure of Pt oxide is different in high-temperature systems, and that catalyst design must take this into account. Fig ure 1. Pt LIII-edge XANES spectra Area vs. Applied voltage for pure H2 at the cathode of Pt/C. MEA temperature: blue circle is 80°C, black circle is 105°C, red circle is 120°C. Fig ure 2. Pt LIII-edge EXAFS Pt-O bond coordination Number vs. Applied voltage for pure H2 at the cathode of Pt/C. MEA temperature: blue triangle is 80°C, black triangle is 105°C, red triangle is 120°C. Acknowledgement This work was supported by a NEDO FC-Platform project commissioned by the New Energy and Industrial Technology Development Organization (NEDO) Reference s : [1] Hideto I.; Koichi I.; Masashi M.; Yoshimi K.; Kazuo K.; Yasuhiko I., J . Am . Chem . Soc ., 2009, 131 (17), 6293-6300. Figure 1

Towards more realistic modelling of sand–rubber mixtures considering shape, deformability, and micro-mechanics

This paper presents realistic discrete element method (DEM) simulations of mixtures of sand and rubber grains. The shape of the grains and the deformability of the rubber are accounted for in the model. A set of 1D compression tests and triaxial compression tests are performed on samples with different rubber contents. It is shown that the model can accurately predict the mixture behaviour at macro-scale. The insights from a micro-mechanical analysis of force chain network, coordination number, and side-wall friction indicate that deformability plays a key role in exhibiting realistic behaviour. Finally, a new criterion is presented to determine the limits of sand-like and rubber-like behaviour.

Yolk-shell nanoparticles with different cores: A molecular dynamics study

In this work, M@void@Pd (M=Ag, Ni, Pt) yolk-shell nanoparticles are studied by classical molecular dynamics simulation. The aim of simulations was to get more information about the relation between thermodynamic stability of the simulated nanoclusters with their core composition. For this purpose, the simulation data was analyzed by various methods including interatomic distance evolution, stability parameter, surface energy, coordination number analysis, conformational changes, and radial distribution function. The results indicated that the interatomic distance evolution and coordination number of the core atoms play the important role in these phenomena, in such a way that the structures with unique physical and chemical properties can be created.

Molecular dynamics study on evaporation of high-salinity wastewater droplet

• Evaporation of wastewater droplets was studied by Molecular Dynamics Simulations. • Influences of ambient temperature, droplet size, and components were considered. • Ion-water interaction, weaker heat transfer, and higher sphericity retard evaporation rate. • Nucleation and dehydration process was monitored by coordination number analysis. • Divalent cations interact with ions and water molecules more actively. Non-equilibrium molecular dynamics simulations (NEMD) are carried out to study the evaporation behaviors of high-salinity wastewater droplets in a high-temperature environment (>500 K). Detailed information on interfacial properties and evaporation characteristics of wastewater droplets containing multiple salts are monitored quantitatively for the first time. To investigate how ions and molecules interact with each other during evaporation, nucleation and growth of ions clusters and the dehydration process are studied by the coordination number analysis. The accuracy of the model is validated by the experimental results, and then effects of ambient temperatures, compositions, and initial sizes are considered. The results show that when the evaporation reaches the steady state in the 600 K ambience, the droplet evaporation rate of wastewater is much smaller than that of the pure water, which can be seen from the evaporation constant (5.58 × 10 −9 m 2 /s for pure water vs 4.60 × 10 −9 m 2 /s for wastewater). After this steady state, the evaporation rate for wastewater is reduced, during which nucleation of ion pairs and dehydration would occur. Ion-water interaction, smaller temperature difference between ambience and droplets, and higher sphericity contribute to the decline in the evaporation rate of wastewater. Nucleation trends of different ion pairs in wastewater vary significantly, and divalent cations (Mg 2+ and Ca 2+ ) play an important role in restricting the motions of water molecules and forming clusters, as shown in the higher average counter ion coordination number. Dehydration of the ions will not occur until most water molecules are evaporated, which is more difficult for divalent ions. Increasing thermostat temperature, decreasing total dissolved solids and decreasing initial sizes are conducive to accelerating the overall evaporation and nucleation rate. The research gives a better understanding of the microscopic mechanisms of wastewater droplet evaporation and further aids in the design and optimization of the thermal desalination process.

Designing Magnetic Semiconductors From a Ferromagnetic Metallic Glass

Utilizing both charge and spin degrees of freedom of electrons simultaneously in magnetic semiconductors promises new device concepts by creating an opportunity to realize data processing, transportation and storage in one single spintronic device. Unlike most of the traditional diluted magnetic semiconductors, which obtain intrinsic ferromagnetism by adding magnetic elements to non-magnetic semiconductors, we attempt to develop new magnetic semiconductors via a metal-semiconductor transition by introducing oxygen into a ferromagnetic Co-Fe-B metallic glass. The atomic structure and electronic structure of the Co-Fe-B-O sample are explored by using first-principles calculations. The total pair correlation functions of both the Co-Fe-B and Co-Fe-B-O samples evidence their glass structures. The bond pair and coordination number analysis together demonstrate that the oxygen addition enables the bond types to change from the dominant metallic bonding in the Co-Fe-B metallic glass to the mixture of metallic, ionic and covalent bonding in the Co-Fe-B-O oxide glass. This results in the localization of electron charge density and the opening of the band gap in the Co-Fe-B-O oxide glass. The density of states suggests the Co-Fe-B-O oxide glass is semiconducting with a band gap of about 1.7 eV, but there are intermediate energy levels in the band gap. Meanwhile, the Co-Fe-B-O oxide glass remains to be ferromagnetic. These results indicate that the Co-Fe-B-O oxide glass is a magnetic semiconductor transferred from a ferromagnetic Co-Fe-B metallic glass, which is further verified by the experimental realization of a Co-Fe-B-O magnetic semiconductor. Furthermore, our calculation results reveal that a hybridization of the 4s/4p, 3d electrons of ferromagnetic Co and Fe atoms and O 2p electrons exists. Such s, p-d exchange interaction is essential to bridge the mutual interaction between the electrical conduction arising from s-like electrons and ferromagnetism supported by 3d electrons in magnetic semiconductors, thereby enabling the control of ferromagnetism by electrical means. Our calculation results represent an important step to gain a deeper understanding of the oxygen addition induced metal-semiconductor transition in an amorphous alloy Co-Fe-B system. We anticipate that our calculation results provide theoretical fundamentals for experimentally transferring many other ferromagnetic amorphous alloys into ferromagnetic semiconductors with attractive magnetoelectric coupling properties.

Relationship between local coordinates and thermal conductivity in amorphous carbon

To determine the correlation between local structure and thermal conductivity of amorphous carbon, we investigated heat conduction in 216-atom systems with different densities (2.0–3.4 g/cm3) using the ab initio molecular dynamics approach. By applying the Allen–Feldman theory with interatomic force constants from ab initio calculations, we report a significant correlation between the thermal conductivity and the density. To clarify which structural characteristics in the high- and low-density cases determine the magnitude of thermal conductivity, we performed geometrical and topological analyses. Coordination number analysis and ring statistics revealed that the sp/sp2/sp3 bond ratios and topological characteristics correlate with density. We also demonstrated that these structural characteristics can be quantified using persistent homology analysis, providing a predictive model of thermal conductivity.

Surface deformation, phase transition and dislocation mechanisms of single crystalline 6H-SiC in oblique nano-cutting

Compared with the conventional orthogonal cutting, the oblique nano-cutting of 6H-SiC by tilting the tool at different angles, i.e., the tool inclination angle, is systematically investigated via molecular dynamics (MD) simulations. Focusing on the deformation mechanism, surface deformation including elastic recovery and deformation layer thickness is studied considering the edge ovalization effect in the cutting plane of oblique cutting. Moreover, the variation of cutting force is also analyzed, which relates to the improvement of processing accuracy and the structural phase transition. In particular, the transition path is clarified by coordination number analysis and virtual X-ray diffraction, which shows that the amorphization process is achieved via an initial transformation from the wurtzite structure to a fivefold coordinated orthorhombic intermediate structure, and then to an amorphous phase. Finally, dislocation analysis reveals that the basal dislocation systems dominate the dislocation behaviors, while in oblique nano-cutting especially at the tool inclination angle of 30°, the dislocation system of {0001}<11¯00> (i.e., the basal 1/3<11¯00> Shockley partial dislocation of 6H-SiC) is more activated due to the inclined-cutting-edge-derived shear stress. Furthermore, stacking faults are also formed beneath the bottom of cutting grooves due to the slip upon fivefold coordinated atoms plane.

NaFSI and NaTFSI Solutions in Ether Solvents from Monoglyme to Poly(ethylene oxide)-A Molecular Dynamics Study.

Classical molecular dynamics simulations have been performed for a series of electrolytes based on sodium bis(fluorosulfonyl)imide or sodium bis(trifluoromethylsulfonyl)imide salts and monoglyme, tetraglyme, and poly(ethylene oxide) as solvents. Structural properties have been assessed through the analysis of coordination numbers and binding patterns. Residence times for Na–O interactions have been used to investigate the stability of solvation shells. Diffusion coefficients of ions and electrical conductivity of the electrolytes have been estimated from molecular dynamics trajectories. Contributions to the total conductivity have been analyzed in order to investigate the role of ion–ion correlations. It has been found that the anion–cation interactions are more probable in the systems with NaTFSI salts. Accordingly, the degree of correlations between ion motions is larger in NaTFSI-based electrolytes.

Effects of Hydration and Temperature on the Microstructure and Transport Properties of Nafion Polyelectrolyte Membrane: A Molecular Dynamics Simulation.

To investigate the effects of temperature and hydration on the microstructure of polymer electrolyte membrane and the transport of water molecules and hydronium ions, molecular dynamics simulations are performed on Nafion 117 for a series of water contents at different temperatures. The interactions among the sulfonate groups, hydronium ions, and water molecules are studied according to the analysis of radial distribution functions and coordination numbers. The sizes and connectivity of water clusters are also discussed, and it is found that the hydration level plays a key role in the phase separation of the membrane. However, the effect of the temperature is slight. When the water content increases from 3.5 to 16, the size of water clusters in the membrane increases, and the clusters connect to each other to form continuous channels for diffusion of water molecules and hydronium ions. The diffusion coefficients are estimated by studying the mean square displacements. The results show that the diffusion of water molecules and hydronium ions are both enhanced by the increase of the temperature and hydration level. Furthermore, the diffusion coefficient of water molecules is always much larger than that of hydronium ions. However, the ratio of the diffusion coefficient of water molecules to that of hydronium ions decreases with the increase of water content.

Automatic 3D cluster modelling of COVID-19 through voxel-based redistribution

Computational analysis of virus dynamics provides a non-contact environment for the study of the vital object. Cluster modelling is an essential step to investigate the properties of a group of viruses, and an automatic approach is required for massive 3D data processing. The morphological complexity of individual virus limits the application of smooth function algorithms with a regular-shaped assumption. This paper proposed a voxel-based redistribution approach to generate the virus cluster with COVID-19 input automatically. Representative elementary volume analysis was performed to address the statistical influence from the digital sample size. Coordination number analysis and surface density measurement were conducted with COVID-19 input and spherical input for comparison. The proposed approach is in natural compatibility with the lattice Boltzmann method for fluid dynamics analysis. A virtual permeation simulation was performed with the COVID-19 cluster and spherical cluster to demonstrate the necessity to include spike protein structure in the cluster modelling.

The Removal Mechanism of Monocrystalline Si in the Process of Double Diamond Abrasive Polishing by Molecular Dynamics Simulation

In order to clarify the mechanism of polishing of double diamond abrasive particles, in this study, the mechanism of material removal and the evolution of single crystal Si workpiece surface under the three-body polishing condition were investigated. The effect of the depth of polishing and the transverse/longitudinal spacing of the double abrasive grains on the three-body polishing were examined. The purpose is to reveal the phase transition, surface morphology, surface damage, material removal rate, temperature, potential energy, and friction force for polishing Si wafer. The analysis of coordination number clarified that the number of phase transition atoms by polishing and abrasion increased with increasing polishing depth and transverse distance of the nanoparticles on the Si work surface, but not especially obvious with increasing longitudinal spacing. Temperature analysis shows that when the polishing depth is 1 nm, the polishing temperature is 456 K, while when the polishing depth is 3 nm, the polishing temperature is 733 K. The temperature difference between the longitudinal group and the transverse group is only 30–40 K. The larger the transverse abrasive grain spacing or the smaller the polishing depth, the smaller the surface roughness; however, the longitudinal abrasive grain spacing has no obvious correlation with the surface roughness.

Radiation damage study on graphite from multiple cascade events in molecular dynamics simulation

Graphite is one kind of materials commonly used in nuclear reactor as neutron moderator and structural material. During the nuclear reactor operation, graphite is bombarded with high dose of radiation, especially neutron. This condition can cause damage to the graphite’s crystal structure which then leads to the change of the graphite’s physical properties. The alteration of graphite properties is undesirable since it affects the operation and limits the lifetime of nuclear reactor. In this research, radiation-induced damages on graphite were investigated using molecular dynamic simulation. Reactive force-field potential was employed as the interatomic potential in a simulation box containing about five hundred thousand carbon atoms. The first cascade was initiated using primary knock-on atom having kinetic energy of 1 keV. Following the first cascade, multiple cascades were performed in the same simulation box to represent the long-term neutron irradiation on graphite and to observe the effect of this cascade repetition on defect production. The cascade simulation was performed at two variation of temperature. The number of defects was identified using coordination number analysis. It was found that the effect of temperature to the number of defects produced is not significant, while the repetition of cascade does increase the number of defects produced at the end of the cascade simulation.

On the structural changes and glass transition temperature relationship during the formation of Re-W metallic glasses

The search for advanced materials has been the main preoccupation of materials scientists for the past years. Binary Re-W metallic glasses (MGs) are very promising candidates for many applications requiring good mechanical proprieties. Molecular Dynamics (MD) simulations with the embedded atom method (EAM) potential have been devoted to investigate the behavior of these materials by exploring their local atomic structure by means of various techniques such as the radial distribution function (RDF), the Voronoi Tessellation Analysis (VTA) and the coordination number (CN). The results showed a splitting in the second peak of RDFs indicating the formation of Re-W metallic glasses. The VTA method showed that the <0,1,10,2> icosahedral Voronoi cluster is the major short-range unit in Re-W MGs. The icosahedral-like cluster abundance is proposed as a measure of vitrification which has been shown to be promoted by the increase of W content. The coordination number analysis showed the existence of transition from low- to high-coordinated atoms occurring at the glass transition temperature. These simulated structural properties were used mainly to study the glass transition temperature Tg using different methods, including the Wendt-Abraham method which is considered as a reference method. Essentially, we suggest the intersection between low- and high-coordinated atom populations to be a measure of Tg.

Study on Local Chemical Orderings in Li3NbO4-Based Positive Electrode Materials with a Disordered Rock-Salt Structure By a Reverse Monte Carlo Modeling

1. Introduction As a positive electrode material for a lithium-ion battery, lithium-rich transition-metal oxides have drawn much attention due to the high discharge capacity. Among the oxides, we have focused on Li1+xM1-xO2 with a disordered rock-salt structure such as Li3NbO4-based solid solution [1]. It is well known that all the cations occupy a same crystallographic site in the crystals. Due to different ionic radii and electronic states of the cations, however, it can be predicted that local structures (non-periodic structures) around different cation species must be distinguishable, and such hidden strucures must affect Li+ behavior in charge and discharge processes. Therefore, some previous works tried to uncover the local structures [2], but the structures are still under debete. This is because the structures without periodicity do not show prominent Bragg peaks in a diffraction profile.From such background, this work investigated local structures of the Li3NbO4-based materials, which can be also denoted as Li1+x(Nb, M)1-xO2, with the disordered rocksalt structure by a reverse Monte Carlo (RMC) modeling using total scattering data. Especially, we paid special attention on Li1.3Nb0.3Fe0.4O2 and Li1.3Nb0.43Ni0.27O2 as typical materials. Based on the modeling results, we discuss effects of the cation species on the local structures.2. Experimental The Li3NbO4-based materials were synthesized by a conventional solid-state reaction method, according to literature [1]. Metal compositions of the samples were analyzed by an inductively coupled plasma atomic emission spectroscopy, and valences of cations were estimated by X-ray absorption near edge structures (BL14B2, SPring-8). Synchrotron X-ray Bragg profiles were collected with BL19B2 (SPring-8), and the crystal structures (average structures) were refined by a Rietveld method. We also measured neutron and synchrotron X-ray total scattering data at NOVA (J-PARC) and BL04B2 (SPring-8), respectively. By using structure factors S(Q) and reduced pair distribution functions G(r) in addition to the Bragg profiles, we performed the RMC modeling with an RMCProfile software under a bond-valence-sum (BVS) constraint. In the modeling, we optimized cation distributions by swapping the cations.3. Results We made a supercell with 1000 atoms from a refined unit cell, and then performed RMC modeling on Li1.3Nb0.3Fe0.4O2 with the disordered rock-salt structure. As a result, we could obtain an atomic configuration which could reproduce X-ray Bragg profile, neutron G(r), neutron and X-ray S(Q). From the atomic configuration, it was found that a local distortion of NbO6 was larger than those of the others (LiO6 and FeO6) in the material. The large distortion should be induced by a smaller ionic radius of Nb5+ and/or a mismatch of electronic state of Nb5+. Furthermore, it was clarified from a coordination-number analysis that Li tended to be surrounded by Nb considerably in the disordered rock-salt structure. Such a tendency was also observed in an atomic configuration of Li1.3Nb0.43Ni0.27O2. From the results, it can be concluded that Li diffusion is disturbed by a cation with a higher valence in the disordered structure.

Study on phase transformation in cutting Ni-base superalloy based on molecular dynamics method

Nickel-based single crystal alloys are widely used in aerospace and other important fields of national defense due to their excellent properties. Phase transformation occurs during high-speed cutting of nickel-based single crystal alloy, which seriously affects the surface quality. It is of great significance to carry out theoretical research on phase transformation for improving the machining quality of nickel-based alloy. In this paper, molecular dynamics method is used to study the nano-cutting of single crystal nickel-based alloy with silicon nitride ceramic tool. The mechanism of phase transformation and the effect of cutting speed on phase transformation in workpieces are studied in detail. The nano-cutting model is established. Morse potential functions for molecular dynamics simulation are calculated, and EAM and Tersoff potential functions are selected. The effect of cutting speed on phase transformation was studied by using radial distribution function, coordination number analysis, common neighbor analysis, and the deep reasons for the sharp change of lattice structure were analyzed from many aspects. Finally, in order to verify the universality of the research results and explore the new properties of compression, nano compression (the same strain rate as the nano cutting process) was simulated. The results show that the increase of cutting speed leads to the increase of hydrostatic stress, the increase of energy in crystal and the rise of cutting temperature. As a result, the change of lattice structure becomes more and more intense, and the conversion rate of different crystal structures increases greatly.