Strength Of Interatomic Bonds Research Articles

The A-Ni chemical bond in AIIINiSb (AIII=Sc, Y, Er) half-Heusler materials triggers the formation of anomalous vacancy defects

Defects exert a profound influence on thermoelectric materials by altering electronic band structures and significantly impacting their performance. Despite being a potentially promising thermoelectric material, the mechanism behind defect formation in half-Heusler (HH) compounds ABX remains unclear, impeding the enhancement of their thermoelectric properties. In this study, we investigated the intrinsic defect formation energies for AⅢNiSb (AⅢ = Sc, Y, Er) and other 9 HH compounds, namely AⅣNiSn (AⅣ = Ti, Zr, Hf), AⅤFeSb (AⅤ = V, Nb, Ta), and AⅣCoSb (AⅣ = Ti, Zr, Hf), using first-principles calculations and thermodynamics. The results reveal that AⅢNiSb (AⅢ = Sc, Y, Er) exhibits anomalous B (Ni) vacancy defects, with their formation energies being significantly lower than those of the corresponding B vacancy defects in the other 9 HH compounds. This anomaly can be attributed to the strength of the A-B bonds, where a decrease in bond strength leads to a decrease in the formation energy of B vacancies. This approach of exploring the influence of interatomic bond strength on defect formation is not only insightful for HH compounds but also holds potential applications in defect studies across various materials, offering a broader perspective on the fundamental mechanisms governing defect formation and stability.

Some strange things about the mechanical properties of glass

Glasses and crystals from the same chemical system mostly share the same interatomic bond strength. Nevertheless, they differ by the arrangement of bonds in space, which gives birth to different atomic packing efficiencies. We show in this review that as far as the elastic moduli and hardness are concerned, the atomic packing density predominates over the bond strength. The shear modulus of crystalline phases is usually much larger than the one of glasses with the same stoichiometric composition, thanks to a more efficient packing of atoms in the former. In contrast, the increase in hardness is quite limited, likely because of the additional contribution of dislocation activity to the deformation processes beneath the indenter in the case of crystals (shear plasticity). We also show that the occurrence of chemical heterogeneities (weak channels) at the mesoscopic scale in glasses, which is often associated with the lack of long range atomic ordering, promotes easy fracture paths and is responsible for the low toughness and fracture surface energy.

Molecular dynamics study of tribological properties of Ni–Cr alloy coatings with different pore shapes

The presence of nanopores with different shapes cannot be avoided during the coating preparation process, and the pore shape is an important factor affecting the coating friction mechanism. This paper applies molecular dynamics to study the tribological properties of Ni–Cr alloy coatings containing spherical, rectangular and ellipsoid-shaped pores. It is found that the coating with spherical pores has the smallest fluctuation of friction coefficient and the shallowest depth of wear scar. The atoms near the rectangular pores are more likely to move towards the corners of the pores due to shear strain, and the stress concentration in the spherical pores is less than that in the rectangular and ellipsoidal pores. The spherical pore has the least effect on the potential energy inside the coating, and the interatomic bond strength is optimal. The ellipsoidal pore is also more effective in insulating the heat transfer to the bottom of the coating, protecting the substrate underneath the coating and prolonging the coating life. Coatings with rectangular pores generate more interstitial atoms during friction, producing Frank dislocation loop and prismatic dislocation loops.

Effects of excess electrons/holes on fracture toughness of single-crystal Si

This study demonstrates that bond strength can be enhanced by injecting excess electrons or holes into a material by electron beam irradiation. To determine the effect of excess electrons/holes on the interatomic bond strength, fracture toughness tests were performed on single-crystal Si micropillars under various electron-beam irradiation conditions. The fracture toughness under electron beam irradiation was 4%–11% higher than that under non-irradiated conditions. In particular, an increase in strength was large in tests performed under hole-injection conditions. Furthermore, in first-principles calculations of the tensile strength of excess electrons/hole-doped Si, the ideal tensile strength monotonically decreased with an injection in excess electrons and increased monotonically with the injection of holes. This is qualitatively consistent with the experimental result that the fracture toughness increases under hole-injection conditions.

Study on interfacial reaction behavior of Sn[sbnd]Ag based lead-free solder with (111) single crystal copper substrate

The morphology and crystal orientation of intermetallic compounds formed by the reaction between SAC305 solder/(111) and SABI333 solder/(111) single crystal copper substrate were investigated. The morphology of Cu6Sn5 at the interface of SAC305 solder/(111) single crystal copper substrate changes from scallop to prismatic with the increase of reflow time. The Cu6Sn5 grains grow parallel to the horizontal direction of the Cu substrate and grow along the vertical direction, and there is an Angle of 60° between different Cu6Sn5 crystals. The calculated b ~ t0.23 relation satisfies the growth kinetics of prismatic Cu6Sn5. In addition, the morphology of Cu6(Sn, In)5 at the interface of SABI333 solder/(111) single crystal copper substrate is between scallop-type and prismatic-type. Cu6(Sn, In)5 grains grow at a certain angle with a single crystal copper substrate due to the addition of In element. Furthermore, it is considered that the deflection mechanism of Cu6(Sn, In)5 grains is controlled by the length and strength of inter-atomic bonds within the grains after the In atom substitution reaction.

Automated Bonding Analysis with Crystal Orbital Hamilton Populations.

Understanding crystalline structures based on their chemical bonding is growing in importance. In this context, chemical bonding can be studied with the Crystal Orbital Hamilton Population (COHP), allowing for quantifying interatomic bond strength. Here we present a new set of tools to automate the calculation of COHP and analyze the results. We use the program packages VASP and LOBSTER, and the Python packages atomate and pymatgen. The analysis produced by our tools includes plots, a textual description, and key data in a machine-readable format. To illustrate those capabilities, we have selected simple test compounds (NaCl, GaN), the oxynitrides BaTaO2 N, CaTaO2 N, and SrTaO2 N, and the thermoelectric material Yb14 Mn1 Sb11 . We show correlations between bond strengths and stabilities in the oxynitrides and the influence of the Mn-Sb bonds on the magnetism in Yb14 Mn1 Sb11 . Our contribution enables high-throughput bonding analysis and will facilitate the use of bonding information for machine learning studies.

Dynamic photoinduced changes of optical characteristics and effect of optical memory in amorphous As–S film-based waveguides

Metastable and transient photoinduced phenomena in as-deposited amorphous AsxS100-x films (15 ≤ x < 30) are studied using a waveguide technique. A detailed investigation of the optical stopping effect is performed. Dynamics of the photostimulated variation of the sub-bandgap mode absorption in the film waveguide is determined by competition of two independent processes: (i) external optical recording with a relatively durable non-volatile memory and (ii) sub-bandgap waveguide mode-initiated erasure by removal of the preceding optical record. Irreversible changes and transient variation of the amorphous AsxS100-x film refractive index under above-bandgap laser illumination, accompanying the stopping effect, are investigated. The transient variation of the film refractive index is due to a photoinduced increase of the interatomic bond strength and a decrease of polarizability, primarily in the vicinity of sulphur atoms.

Liquid zinc penetration induced intergranular brittle cracking in resistance spot welding of galvannealed advanced high strength steel

This study aims to explore the mode of Zn transportation and the failure mechanism of cracking associated with liquid metal embrittlement (LME) using fractography as the key technique. A three-point bend test was performed on a TRIP steel resistance spot weld to open the LME crack in the form of a free fracture surface for the fractographic investigation. The presence of liquid Zn on the fracture surface was revealed by the Fe-Zn phase transformation and the spike-like morphology of the residual Zn, confirming that the mode of Zn transportation in LME cracks was liquid penetration through the austenite grain boundary. In addition, the fractography of the bend test samples and electron backscattered diffraction of the cracks revealed the failure mode of the LME crack as a complete intergranular brittle fracture without the generation of any microplasticity. Thus, the underlying failure mechanism of cracking in Zn-LME can be explained by the Stoloff-Johnson-Westwood-Kamdar brittle fracture model induced by the decohesion of interatomic bonds. Overall, a dramatic reduction in the interatomic bond strength by lowering the surface energy of the grain boundary with liquid Zn penetration causes the decohesion-induced intergranular brittle cracking.

ОСОБЕННОСТИ ЭВОЛЮЦИИ НАНОМАСШТАБНЫХ ХАРАКТЕРИСТИК МЕТАЛЛА ПРИ НАГРУЖЕНИИ ТЕРМИЧЕСКИМИ ЦИКЛАМИ

Актуальность исследования обусловлена отсутствием экспериментальных данных, устанавливающих связь между субмикроскопическими свойствами (свойствами III рода) и макроскопическими свойствами I рода. Такая взаимосвязанность, являющаяся фактором влиянияна отношение «микроструктура–прочность», может способствовать дальнейшим успехам в решении вопросов ресурса. Цель исследования заключается в установлении влияния циклических термических нагрузок на среднеквадратичные смещения атомов как показатель прочности межатомных связей и микроповрежденности металла пароперегревательных труб. Объектом исследования являются образцы из околошовных зон однородного сварного шва, выполненного из жаропрочной перлитной стали 12Х1МФ. Методы: физическое моделирование условий эксплуатации путем воздействия на образцы циклами термической нагрузки в электропечи МИМП-10УЭ, рентгенометрия образцов, оценка внутренних структурных напряжений на рентгеновских дифрактометрах ДРОН, морфология поверхности с помощью портативного электронного микроскопа типа PENSCKOPE. Результаты.Установлено влияние циклических термических нагрузок на среднеквадратичные смещения атомов. Показано, что в результате термического влияния прочность межатомных связей увеличивается. Проиллюстрирована корреляция между субмикро- и макроскопическими характеристиками прочности, и показано, что амплитуда тепловых колебаний атомов, являясь характеристикой прочности межатомных связей, может быть диагностическим признаком накопления и развития повреждаемости металла. Уменьшение амплитуды среднеквадратичных смещений атомов при термоциклировании объяснено на основе гипотезы о возникновении твердых растворов замещения в результате процесса азотирования поверхности молекулярным азотом атмосферного воздуха. В рамках этой гипотезы показано, что одним из механизмов осцилляции внутренних напряжений I рода при термоциклировании может быть процесс азотирования поверхности, приводящий к организации в многокомпонентных легированных сталях сложных связей «металл–неметалл», направленных на поддержание устойчивости системы твердых растворов.

Structure and conductivity of perovskite Li0.355La0.35Sr0.3Ti0.995M0.005O3 (M = Al, Co and In) ceramics

Perovskite-type solid electrolyte Li0.355La0.35Sr0.3Ti0.995M0.005O3 (LLSTM, M = Al, Co and In) ceramics were prepared via a conventional solid phase reaction method. The conductivities and microstructure of LLSTM samples were systematically investigated by scanning electron microscopy (SEM), Raman spectroscope, XRD, X-ray photoelectron spectroscopy (XPS) and AC impedance spectroscope. All samples exhibited a cubic perovskite structure, meanwhile, lattice parameter increased when the larger B-site ions were substituted compared to Ti4+ and vice versa. It was found that the shift of characteristic peaks of Ti4+ from Raman and XPS spectra are connected to their different bond strength as the cation substitutions with different ionic radii. The ionic conductivity decreased with increasing the radii of B-site ions due to the change of interatomic bond strength. Besides, lattice parameter changed companying with a Ti(M)-O octahedron distortion and bottle sizes difference also have an influence on conductivity. It was shown that all samples at room temperature have a σt at a magnitude of 10−5 S/cm and σe at 10−11 S/cm, indicating that the LLSTM samples are good lithium conductors. The findings would deepen the understanding of the relations among B-site cation substitution, ionic conduction and microstructure in perovskite ionic conductors.

Ab initio study of ionic nature of 0.75AgI:0.25AgCl

Ab initio calculations based on density functional theory are performed for zinc-blende structured new host 0.75AgI:0.25AgCl. Eight configurations are simulated for different positions of Cl atoms, and they are divided into three sets of configurations. Similar calculations are also performed for zinc blende β-AgI. Bond lengths are changed and p-d hybridization is observed in all configurations. Ionic nature of atomic bonds is analyzed by the ionicity factor. The charge density analysis also exhibits the ionic and least covalent nature of bonds of AgI and AgCl atoms. The structural parameters are calculated to observe the bulk modulus. Crystal orbital overlap population analysis explains the inter-atomic bond strength which explains the bond breaking energy and activation energy of all configurations.

Quasiparticle approach to diffusional atomic scale self-assembly of complex structures: from disorder to complex crystals and double-helix polymers

AbstractA self-organisation is an universal phenomenon in nature and, in particular, is highly important in materials systems. Our goal was to develop a new theory that provides a computationally effective approach to this problem. In this paper a quasiparticle theory of a diffusional self-organisation of atoms in continuum space during the diffusional time scale has been introduced. This became possible due to two novelties, a concept of quasiparticles, fratons, used for a description of dynamic degrees of freedom and model Hamiltonian taking into account a directionality, length and strength of interatomic bonds. To illustrate a predictive power and achievable level of complexity of self-assembled structures, the challenging cases of self-assembling of the diamond, zinc-blende, helix and double-helix structures, from a random atomic distribution, have been successfully modelled. This approach opens a way to model a self-assembling of complex atomic and molecular structures in the atomic scale during diffusional time.

Relation between the strength and dimensionality of defect-free carbon crystals.

On the basis of ab initio simulations, the value of strength of interatomic bonds in one-, two- and three-dimensional carbon crystals is obtained. It is shown that decreasing in dimensionality of crystal gives rise to nearly linear increase in strength of atomic bonds. It is ascertained that growth of strength of the crystal with a decrease in its dimensionality is due to both a reduction in coordination number of atom and increase in the angle between the directions of atomic bonds. Based on these data, it is substantiated that the one-dimensional (1D) crystals have maximum strength, and strength of carbyne is the absolute upper limit of strength of materials.

Thermal transport across graphene and single layer hexagonal boron nitride

As the dimensions of nanocircuits and nanoelectronics shrink, thermal energies are being generated in more confined spaces, making it extremely important and urgent to explore for efficient heat dissipation pathways. In this work, the phonon energy transport across graphene and hexagonal boron-nitride (h-BN) interface is studied using classic molecular dynamics simulations. Effects of temperature, interatomic bond strength, heat flux direction, and functionalization on interfacial thermal transport are investigated. It is found out that by hydrogenating graphene in the hybrid structure, the interfacial thermal resistance (R) between graphene and h-BN can be reduced by 76.3%, indicating an effective approach to manipulate the interfacial thermal transport. Improved in-plane/out-of-plane phonon couplings and broadened phonon channels are observed in the hydrogenated graphene system by analyzing its phonon power spectra. The reported R results monotonically decrease with temperature and interatomic bond strengths. No thermal rectification phenomenon is observed in this interfacial thermal transport. Results reported in this work give the fundamental knowledge on graphene and h-BN thermal transport and provide rational guidelines for next generation thermal interface material designs.

Evaluation of Mechanical Properties Variations for Kr Ion‐Irradiated 6H‐SiC by Nanoindentation Methods

Nanoindentation experiments were performed to investigate the irradiation effects on the mechanical properties of 6H‐SiC irradiated by 4 MeV Kr ions at high fluences from room temperature (RT) to 550°C. The irradiation temperature is the primary factor that affects modifications of the comprehensive mechanical properties, while the effect of the fluence is less significant. Elastic modulus and hardness decrease drastically for RT‐irradiated samples, but they almost recover for elevated temperature samples, with hardness slightly higher than its original value. The hardness increases first and then decreases with increasing temperature, and the elastic modulus decreases linearly as the swelling increases. Meyer's index is related to the indentation size effect of hardness and the magnitude of the lattice damage. The ratio of irreversible work is associated with the degree of elastic recovery and the ratio of hardness to elastic modulus of SiC. Compared with the unirradiated value, fracture toughness changes slightly for RT irradiation, while increasing significantly for elevated temperature irradiation and has the same variation tendency of hardness. Results indicate that mechanical properties change with the variations of interatomic bond strength, dislocation mobility, and the behavior of crack propagation, which is strongly affected by the defects induced by heavy‐ion irradiation.

The effect of structural degrees of freedom on bonding and strength characteristics of molybdenum disilicide

Tensile test in MoSi 2 with C11 b structure along the [001] direction is simulated from first principles using the full-potential linearized augmented plane wave method. A full relaxation of all external and internal structural parameters is performed, and influence of each relaxation process on energetics, strength and behavior of interatomic bonds is investigated in detail. It turns out that for a correct description of the phenomena studied, as e.g. tension–compression asymmetry or the behavior of the interatomic bonds, full relaxation of all structural parameters must be performed.

Local dynamic deformation of the superconducting CuO2 plane in the Nd2 − x Ce x CuO4 + δ compound

The local structure of the electron-doped high-temperature superconductor Nd2 − x Ce x CuO4 + δ has been investigated by EXAFS spectroscopy using synchrotron radiation in the temperature range 5–300 K. The radii, coordination numbers, and Debye-Waller factors of the nearest coordination spheres of the copper, neodymium, and cerium local environment have been obtained. The Einstein temperatures, characterizing the strength of Cu-O, Nd-O, and Ce-O interatomic bonds have been determined. The dynamic local deformation of the superconducting CuO2 plane in the form of vibrations of some part of oxygen ions in a double-well potential due to the difference in the electronic filling of neighboring CuO4 complexes has been established.

2-Point Bending Strength of Glass Fibers

Failure strains of some glass fibers were measured by 2-point bending test at liquid nitrogen temperature. The failure strength was estimated from failure strain and Young's modulus of glass. At a face-plate rate of 50μm/sec, failure strains were 12% (failure strength is 8.6GPa) for silica glass, 15% (10GPa) for soda-lime glass and 16% (10GPa) for lead glass, respectively. High failure strength of lead glass fiber suggests that 2-point bending strength of glass fiber is determined not only from interatomic bond strength but also from inelastic energy dissipation on fracture.

Application of a physically consistent theory of brittle fracture

Abstract This paper examines the profile and associated stress field of an equilibrium slit crack in a brittle solid using a mesoscopic fracture model. The model is based on a physically consistent description of crack profiles in solids, developed from an analysis by Chan et al. in which the forms of intersurface cohesive forces are used explicitly. The mesoscopic nature of the problem arises from the embedding of the nonlinear and non-monotonic atomic-scale intersurface cohesive forces and length scales into a classical formulation of the elastic fracture problem. The analysis is used to calculate the full crack profile, encompassing three asymptotic limits: the near-tip Barenblatt zone, a transition zone in which the cohesive forces are still active and the far-field elastic classical zone. The analysis is also used to calculate the stress field surrounding the crack, revealing a finite maximum at the crack tip associated with the interatomic bond strength. A result of the analysis is that very small cracks (such as might occur in microelectronic circuits) have suppressed stress fields that cannot be related to the equilibrium condition of Griffith thermodynamics by the Irwin crack extension exercise and that vary with crack size. The Griffith equilibrium condition itself is unaffected by the modified stress fields and is uniquely defined by the integral of the cohesive forces acting across the faces of the crack.

Application of a physically consistent theory of brittle fracture

Abstract This paper examines the profile and associated stress field of an equilibrium slit crack in a brittle solid using a mesoscopic fracture model. The model is based on a physically consistent description of crack profiles in solids, developed from an analysis by Chan et al. in which the forms of intersurface cohesive forces are used explicitly. The mesoscopic nature of the problem arises from the embedding of the nonlinear and non-monotonic atomic-scale intersurface cohesive forces and length scales into a classical formulation of the elastic fracture problem. The analysis is used to calculate the full crack profile, encompassing three asymptotic limits: the near-tip Barenblatt zone, a transition zone in which the cohesive forces are still active and the far-field elastic classical zone. The analysis is also used to calculate the stress field surrounding the crack, revealing a finite maximum at the crack tip associated with the interatomic bond strength. A result of the analysis is that very small c...