Atomic Bonding Research Articles

Asymmetric nanofracture in WS2 for its local toughness anisotropy

Fracture in crystal lattices usually occurs with discrete atomic bond breakages around the crack tip. WS2 involves three-layer atomic structures, where the atomic stress near the crack front exhibits thickness dependence and significantly relies on the local distortion of lattice geometry. We show that the T-stress obtained by over-deterministic methods, and the continuum circumferential stress, are limited in predicting the nanocrack kinking of WS2 strips by molecular dynamics simulations. As the far-field displacement loads, the T-stress initially increases in negative, followed by a slight jump at the initiation of kinking, and the continuum circumferential stress cannot accurately capture the variation of atomic stresses at the crack tip. This can be attributed to the local anisotropy in atomic lattices, and the crack preferentially extends in the zigzag direction of the local maximum energy release rate. Our work might provide insights into the fabrication and assembly of WS2 nanodevices.

On tricyclic graphs with maximum atom–bond sum–connectivity index

The sum-connectivity, Randić, and atom-bond connectivity indices have a prominent place among those topological indices that depend on the graph's vertex degrees. The ABS (atom-bond sum-connectivity) index is a variant of all the aforementioned three indices, which was recently put forward. Let T(n) be the class of all connected tricyclic graphs of order n. Recently, the problem of determining graphs from T(n) having the least possible value of the ABS index was solved in (Zuo et al., 2024 [39]) for the case when the maximum degree of the considered graphs does not exceed 4. The present paper addresses the problem of finding graphs from T(n) having the largest possible value of the ABS index for n≥5.

The Nature of Pyroelectric Polarity

The concept of spontaneous polarization in the pyroelectrics is called into a question, since omnipresent free electric charges make impossible to maintain any equilibrium and time-stable polarized state. We conjecture in this paper that pyroelectricity in polar crystals and piezoelectricity in polar-neutral crystals are due to hybridized ionic-covalent polarity-activating bonds. When they are in non-excited state, these bonds do not produce electric field, yet they are capable of generating the electric response to uniform non-electric influence, e.g., heat, pressure, etc. This response is described by some models of different electric moments. Different contributors to these moments can be measured using partial limitation of crystal thermal strain. In fact, the proposed approach modifies and extends the known concept of spontaneous polarization. In this context, ferroelectrics are distinguished by the fact that, in the electric field, they reorient their polarity-activating inter-atomic bonds with a non-linear response and hysteresis.

Mechanical Interatomic Bond Formation in Ethanol and Methanol-Ethanol Mixture by Laser-Driven Shock Waves.

Molecules, which were predicted to be produced by C-C or C-O bond formation between ethanol molecules induced by a laser-driven shock wave, were identified by gas chromatography-mass spectrometry. Moreover, the laser irradiation of a methanol-ethanol mixture revealed the formation of C-C and C-O bonds between both components. Particularly, four hemiacetals (methoxymethanol, 1-methoxyethanol, ethoxymethanol, and 1-ethoxyethanol) were identified in the Ar-saturated alcohol samples, whereas acetalization dominated sufficiently in the CO2-saturated samples, significantly reducing the hemiacetals. It was verified that some molecules were produced by the dropout of an ethanol part during the C-C or C-O bond formation, supporting the contribution of laser-driven shock waves.

Stress-induced intersecting stacking faults and shear antiphase boundary in Zr5Ge4 second phase precipitate embedded in Ge-modified Zircaloy-4

Secondary phase precipitates are vital to control mechanical, corrosion and irradiation response of the multiphase alloy systems. This work reports the mechanical response of an ordered complex intermetallic Zr5Ge4 precipitate during hot working of the experimental Zircaloy-4 modified with dilute Ge addition. Atomic scale insight is provided into the formation mechanism of straight and circular stacking faults and shear antiphase boundary in Zr5Ge4 precipitate. Two types of stacking faults, having displacement vectors 1/3[100] and 1/3[110] with small components along the c-axis, come across and form a distinct region on the (001) surface composed of a zigzag atomic arrangement different from the parent crystal. Besides this, a shear antiphase boundary along the Zr5Ge4/fcc-Zr interface is analysed and concomitant generation of nanotwins is evidenced by the streaking effect in the associated fast Fourier transform (FFT) pattern. By analysing the distortion and stacking faults in the surrounding fcc-Zr phase, comments are made on the role of external stresses in generating the aforementioned planar defects. The relative activity of two types of displacement vectors observed in Zr5Ge4 precipitate is discussed on the basis of the nature of the atomic bond.

Pressure-induced phase transition in nanostructured cation-deficient Zn0.34Fe2.53☐0.13O4 ferrite

The crystal structure and vibrational spectra of cation-deficient nanostructured zinс ferrite Zn0.34Fe2.53☐0.13O4 (where ☐ denotes the cation vacancies) have been studied using X-ray diffraction and Raman spectroscopy methods in the pressure range of 0–34 GPa. Our results indicate a phase transition from the initial cubic phase with space group Fd3‾m to a high-pressure phase with orthorhombic symmetry of Bbmm at pressures above 18 GPa. This phase transition is accompanied by changes in lattice parameters, unit cell volume, interatomic bond lengths, and vibration mode frequencies.

Local structural modelling and local pair distribution function analysis for Zr–Pt metallic glass

In disordered glass structures, the structural modelling and analyses based on local experimental data are not yet established. Here we investigate the icosahedral short-range order (SRO) in a Zr–Pt metallic glass using local structural modelling, which is a reverse Monte Carlo simulation dedicated to two-dimensional angstrom-beam electron diffraction (ABED) patterns, and local pair distribution function (PDF) analysis. The local structural modelling invariably leads to the icosahedral SRO atomic configurations that are similarly distorted by starting from some different initial configurations. Furthermore, the SRO configurations with 11–13 coordination numbers reproduce almost identical ABED patterns, indicating that these SRO structures are similar to each other. Further local PDF analysis explicitly indicates the presence of the wide distribution of atomic bond distances, which is comparable to the global PDF profile, even at the SRO level. The SRO models based on the conventional MD simulation can be strengthened by comparison with those obtained by the present local structural modelling and local PDF analysis based on the ABED data.

Nano-cutting mechanism of ion implantation-modified SiC: reducing subsurface damage expansion and abrasive wear

This study utilized ion implantation to modify the material properties of silicon carbide (SiC) to mitigate subsurface damage during SiC machining. The paper analyzed the mechanism of hydrogen ion implantation on the machining performance of SiC at the atomic scale. A molecular dynamics model of nanoscale cutting of an ion-implanted SiC workpiece using a non-rigid regular tetrakaidecahedral diamond abrasive grain was established. The study investigated the effects of ion implantation on crystal structure phase transformation, dislocation nucleation, and defect structure evolution. Results showed ion implantation modification decreased the extension depth of amorphous structures in the subsurface layer, thereby enhancing the surface and subsurface integrity of the SiC workpiece. Additionally, dislocation extension length and volume within the lattice structure were lower in the ion-implanted workpiece compared to non-implanted ones. Phase transformation, compressive pressure, and cutting stress of the lattice in the shear region per unit volume were lower in the ion-implanted workpiece than the non-implanted one. Taking the diamond abrasive grain as the research subject, the mechanism of grain wear under ion implantation was explored. Grain expansion, compression, and atomic volumetric strain wear rate were higher in the non-implanted workpiece versus implanted ones. Under shear extrusion of the SiC workpiece, dangling bonds of atoms in the diamond grain were unstable, resulting in graphitization of the diamond structure at elevated temperatures. This study established a solid theoretical and practical foundation for realizing non-destructive machining at the atomic scale, encompassing both theoretical principles and practical applications.

A mean field description of steady state isotropic structural superplastic deformation

A model developed previously to treat steady state isotropic superplastic deformation turned out to be of generic value and relevant to many classes of materials from metallic materials, ceramics, intermetallic compounds, composites, bulk metallic glasses, and geological materials. The present paper demonstrates the applicability of the concept of “oblate spheroidal ensembles of atoms containing quantified excess free volume present in a general grain boundary” to predict quantitatively the response of general, high-angle grain boundaries when subjected to external stimuli, e.g., an external stress, irrespective of the nature of the atomic bonds (metallic, ionic, or covalent) in preference to purely geometric descriptions of the grain boundary. The emergence of “oblate spheroids” as a response to an external stimulus is regarded in this analysis as self-organizing and a basic phenomenon that cuts across material classes and the nature of the chemical bonds.

Electronic structures, elastic and anisotropic properties of TiAl3 intermetallics doped with Nb

The elastic and anisotropic properties of TiAl3 intermetallics doped with Nb are investigated systematically based on the electronic structures calculation. It shows that the Nb atoms are preferentially to substitute Ti sites forming a stable crystal structure. The DOS of Nb–doped TiAl3 suggests that there is a pseudogap in (Ti18–x + Nbx)Al54. It reinforces atomic covalent bonds while the metallic bond in Ti18(Al54–x + Nbx) is increased. The predicted elastic properties of Nb–doped TiAl3 implies that its strength can be reinforced when the Ti sites substituted by Nb whereas the ductility of the doped intermetallics can be ameliorated when Al sites substituted by Nb. The anisotropy of Young's modulus and shear modulus indicate the uniform deformation ability of (Ti18–x + Nbx)Al54 is better than that of Ti18(Al54–x + Nbx). Poisson's ratio of Ti18Al54 and Ti18(Al51+Nb3) suggest an auxetic feature may be existed when a tensile stress is applied on a specific direction.

First-principles study of Ni clusters growth on graphene with a vacancy

In this work, we performed first-principles calculations to study the interactions of Nin clusters (n = 2-5) with graphene. Nin clusters were adsorbed on pristine graphene and graphene with a vacancy. We observed that the adsorption energy is significantly lowered when graphene has a single vacancy. The single vacancy gives place to a charge redistribution that favors chemisorption. The dangling bonds of the carbon atoms produced by the vacancy increase the magnetic moment of the C atoms around the hole induced by the Ni clusters. We found that the situation is very different when the Ni cluster is adsorbed with atoms on both sides of the vacancy. We consider the cases in which one of the Ni atoms is located on one side of the graphene sheet and the rest on the other, Nin,1. The adsorption energy for Ni3,1 and Ni4,1 clusters are slightly larger than when the whole cluster is chemisorbed on one side only, but the charge redistribution, occurring on both sides of the graphene, increases the possibility to adsorb other molecules. For all cases, we analyzed the electronic density of states to account for the electronic changes on the graphene sheet as a function of the size of the Nin cluster. Finally, the Bader effective charges were computed to follow the charge transfer between Nin clusters and the graphene atoms.

Pressure-induced evolution of structures and phase transition of technetium diboride

Using the particle swarm optimization algorithm, we conducted an extensive search for the high-pressure stable structure of technetium diboride (TcB2) within the pressure range of 0–400 GPa. At zero pressure, the P63/mmc (hP6-TcB2) structure is considered the ground state configuration. As the pressure increases, a structural transition from hP6-TcB2 to P6/mmm (hP3-TcB2) occurs at approximately 174.9 GPa. We discuss the bonding between the two distinct phases and analyze the contribution of different atomic bonds to maintaining their structural stability. Meanwhile, the temperature–pressure phase diagram of TcB2 was successfully determined for the first time through the quasi-harmonic approximation method. It is predicted that the transition pressure from hP6-TcB2 to hP3-TcB2 can be reduced to about 164 GPa at a room temperature of 300 K. These results provide valuable insights into the behavior of TcB2 under different temperature and pressure conditions and open up new possibilities for exploring its potential applications in a variety of environments.

Analyze the temperature-dependent elastic properties of single-walled boron nitride nanotubes by a modified energy method

The elastic properties of boron nitride nanotubes (BNNTs) were investigated utilizing an enhanced energy method. By considering small deformations and applying the principle of minimum potential energy, the variations in atomic bonds and bond angles within the nanotube structure were determined. The modified model incorporated the contribution of inversion energy to the overall potential energy of the system, leading to the derivation of analytical expressions for the Young's modulus, shear modulus, and strain energy of both armchair and zigzag BNNTs under varying temperatures. The results indicate that compared to zigzag BNNTs, the impact of inversion energy on the elastic constants of armchair BNNTs is more significant, especially at small diameters (<1 nm). In thermal environment, this study demonstrates that the change in Young's modulus of BNNTs is lower than that of carbon nanotubes (CNTs), confirming the superior thermal stability of BNNTs over CNTs. Furthermore, molecular structure mechanics (MSM) and continuum mechanics models were employed to analyze the strain energy of BNNTs. The effects of different bonds, bond angles, and inversion angles on strain energy were analyzed in a thermal environment, revealing distinct differences between the two types of BNNTs. These findings provide more accurate theoretical guidance for thermal applications based on the stretching of BNNTs.

Ni-Co Complex Ionic Synergistically Modifying Octahedron Lattice of Cordierite Ceramics for the Application of 5G Microwave-Millimeter-wave Antennas.

In this work, phase-pure Mg1.8(Ni1-xCox)0.2Al4Si5O18 (0 ≤ x ≤ 1) ceramics were synthesized by a high-temperature solid-state method. On the basis of Rietveld refinement data of X-ray powder diffraction and Phillips-Vechten-Levine theory, the atomic ionicity, lattice energy, and bond energy of the compound were calculated to explore their influence on the microwave dielectric properties of ceramics. The Mg1.8Ni0.1Co0.1Al4Si5O18 (x = 0.5) ceramic exhibited the best microwave dielectric properties: εr = 4.44, Qf = 73 539 GHz@13 GHz, and τf = -23.9 ppm/°C. (Ni1-xCox)2+ complex ionic doping, compared with only Ni2+ or Co2+, is beneficial for improving the symmetry of [Si4Al2O18] hexagonal rings and reducing distortion. Subsequently, 8 wt % TiO2 was added to Mg1.8Ni0.1Co0.1Al4Si5O18, resulting in a near-zero τf and high Qf values for the composite ceramic, with εr = 5.22, Qf = 58 449 GHz@13 GHz, and τf = -2.06 ppm/°C. Finally, a 5G millimeter-wave antenna with a central operating frequency of 25.52 GHz was designed and fabricated using the Mg1.8Ni0.1Co0.1Al4Si5O18-8 wt % TiO2 ceramics. Operating in the 24.7-26.0 GHz range, it demonstrated favorable radiation characteristics with a simulated efficiency of 85.2% and a gain of 4.58 dBi. The antenna's performance confirms the high potential of the cordierite composite for application in 5G communication systems.

All-electron basis sets for H to Xe specific for ZORA calculations: Applications in atoms and molecules

Abstract A segmented basis set of quadruple zeta valence quality plus polarization functions (QZP) for H through Xe was developed to be used in conjunction with the ZORA Hamiltonian. This set was augmented with diffuse functions to describe electrons farther away from the nuclei adequately. Using the ZORA-CCSD(T)/QZP-ZORA theoretical model, atomic ionization energies and bond lengths, harmonic vibrational frequencies, and atomization energies of some molecules were calculated. The addition of core-valence corrections has been shown to improve the agreement between theoretical and experimental results for molecular properties. For atomization energies, a similar observation emerges when considering spin-orbit couplings. With the augmented QZP-ZORA set, static mean dipole polarizabilities of a set of atoms were calculated and compared with previously published recommended and experimental values. Performance evaluations of the ZORA and Douglas–Kroll–Hess Hamiltonians were made for each property studied.

Raman peak shift and broadening in crystalline nanoparticles with lattice impurities

The effect of point-like lattice impurities on nanoparticle Raman spectra is studied using both numerical and analytical methods. Particular cases of replacement atoms of various masses, vacancies, and disorder in interatomic bonds are considered. It is shown that the disorder leads not only to the broadening of optical phonon lines but also to the shift of the corresponding Raman peak. The latter can be either positive (i.e., blueshift) or negative (redshift) depending on the type of impurities. Thus there is an additional contribution to the well-known redshift that occurs due to the size-quantization (confinement) effect. Considering nanometer-sized diamond particles as a representative example, we show that the broadening and the shift are, as a rule, of the same order of magnitude. The results are discussed in the framework of the self-consistent T-matrix approach. It is argued that both effects should be considered for accurate treatment of experimental Raman spectra. Simple recipes to do so are formulated for several important cases including NV centers in nanodiamonds.

Modeling from the first principles of the electronic properties of compositions of REE as precursors of high-temperature superconductors

Modeling of the first principles of the electronic properties of complex oxides of rare earth elements (BaY2O4, BaGd2O4, BaLu2O4) as precursors of high-temperature superconductors has been performed. The VASP software package was used as a modeling environment, in particular the method of coupled plane waves (PAW method), which allows us to obtain fairly accurate results for calculating the electron density and band structure. From the analysis of the obtained band energy structure, it follows that the studied REE oxides have a band gap width Eg = 3.29–3.84 eV, which is characteristic for dielectric materials. The studied compounds based on these rare earth elements selected from the yttrium (Y, La, Gd–Lu) and cerium (Ce–Eu) groups are characterized by an increase in Fermi energy and a decrease in the band gap as the atomic number (39, 64, 71) of the element in the periodic table increases. A method for modeling the quantum layers of the studied materials by simulating the restriction of the crystal structure along one of the coordinate axes is proposed. This representation approximates the model of the crystal lattice of REE oxides to the situation of analyzing a quantum layer whose thickness is equal to the size of the crystal cell along the specified axis. The rupture of atomic bonds in a crystal is simulated by increasing the distance between atomic layers along this axis to values at which the value of free energy is stabilized. In the quantum layer of rare earth element oxide (with its thickness close to 1 nm), a wider range of energy values is formed in which electrons are distributed than is observed in the continuous version, and the expansion of the electron distribution area extends to the energy levels of the band gap. This is explained by the fact that the geometric discretization of nanoscale structures determines the discreteness of the quantum-dimensional energy spectrum.

Increase in interplanar distances and formation of amorphous shear bands in deformed diamond

Amorphous transformation-deformation bands have been observed in diamond under cyclic loading (at planetary ball milling) near the graphite-diamond equilibrium line at temperatures below the Debye temperature. The maximum stresses and temperature in the diamond do not exceed 6 GPa and 420 K, respectively. These bands add to the set of plastic deformation mechanisms in diamond. TEM methods and conventional X-rays were used to investigate the mechanisms of plastic deformation of diamond. The observed mechanisms include amorphous deformation bands, bond breaking, twin formation, and phase transitions of diamond-lonsdaleite and diamond-onions. The increased interplanar distances provide evidence of the plastic deformation mechanism due to bond breaking. The distances of 0.222 and 0.255 nm are significantly larger than the initial value of 0.206 nm, which is characteristic of d111 diamond. This increase in distance cannot be attributed to lattice expansion caused by point defects, but rather to the breakage of interatomic bonds.

Unveiling interatomic distances influencing the reaction coordinates in alanine dipeptide isomerization: An explainable deep learning approach.

The present work shows that the free energy landscape associated with alanine dipeptide isomerization can be effectively represented by specific interatomic distances without explicit reference to dihedral angles. Conventionally, two stable states of alanine dipeptide in vacuum, i.e., C7eq (β-sheet structure) and C7ax (left handed α-helix structure), have been primarily characterized using the main chain dihedral angles, φ (C-N-Cα-C) and ψ (N-Cα-C-N). However, our recent deep learning combined with the "Explainable AI" (XAI) framework has shown that the transition state can be adequately captured by a free energy landscape using φ and θ (O-C-N-Cα) [Kikutsuji et al., J. Chem. Phys. 156, 154108 (2022)]. In the perspective of extending these insights to other collective variables, a more detailed characterization of the transition state is required. In this work, we employ interatomic distances and bond angles as input variables for deep learning rather than the conventional and more elaborate dihedral angles. Our approach utilizes deep learning to investigate whether changes in the main chain dihedral angle can be expressed in terms of interatomic distances and bond angles. Furthermore, by incorporating XAI into our predictive analysis, we quantified the importance of each input variable and succeeded in clarifying the specific interatomic distance that affects the transition state. The results indicate that constructing a free energy landscape based on the identified interatomic distance can clearly distinguish between the two stable states and provide a comprehensive explanation for the energy barrier crossing.

Material analysis of tool feed on scrap machines using the vibration method

Flexibility comes from the cutting force generated when the workpiece and tool react and are moved to different areas of the scrap machine. The chisel will get damaged as a result. The material and cutting speed that are used can cause damage. Given this, further studies employing the vibration method are required to determine the ways in which material affects the speed at which scrap is chopped. PVC, iron, and aluminum 5052 were the materials used in this investigation. The cutting rotational speeds varied from 32 to 80 m/min. To measure vibration, the accelerometer is positioned along the x, y, and z axes. The measurement outputs of the accelerometer are connected to the FFT Analyzer, which performs analysis using Matlab. When comparing cutting speeds above or below 50 m/min, the research results indicate that the x-axis has the largest amplitude and the most form variants. The most widely used material is PVC, which is followed by iron and aluminum. This is because, unlike aluminum and iron, which have microstructures in the form of crystal grains, PVC is a thermoplastic polymer with a microstructure made of chain molecules. Because all of the cutting energy is used in the frictional action between the chip and the workpiece when the tool is being used, the high frequency is the result. As a result, the friction on the sliding plane is breaking up atomic or molecular bonds. Additionally, the cutting force exerts a significant amount of pressure on the tool's wearing active surface