Elastic Calculations Research Articles

First-principles study on the interfacial interactions between h-BN and Si3N4

Abstract High-performance ceramics, especially h-BN-based ceramics, are widely used in the metallurgical field. The interface state of h-BN-based ceramic composites, including chemical reactions, molecular diffusion, and interface structure changes, will greatly affect the properties of composite materials. Herein, taking Si3N4/BN composites as a representative case, their interfacial interactions were investigated by first-principles calculations. First, the structural and electronic properties and elastic modulus of bulk Si3N4 and h-BN were calculated. Then, the interface mismatch relationship and interface models of Si3N4/BN were studied and established. Finally, the interface bond structure of Si3N4/BN was analyzed by charge density and state density calculations. The results showed that the band gap of bulk Si3N4 and h-BN was 4.18 and 4.24 eV, respectively. Besides, bulk h-BN exhibited better compression performance and resistance to deformation than Si3N4 based on elastic modulus calculation. Therefore, h-BN was used as a substrate, and when interface mismatch is 1.3%, good matching and bonding at the interface layer can be obtained. Based on this, two interface models of Si3N4(100)/BN(002) were established, which were named the B-NSi interface and Si-NB interface. The BN/Si3N₄ interface exhibited strong van der Waals interactions, and the charge transfer from Si3N4 to h-BN was observed, which indicate that the weak covalent bond also exists in the BN/Si3N4 interface. The low interface energy indicates that the formed interface is relatively stable, which is beneficial for applications requiring high thermal and mechanical stability. This work provides valuable insights into the interfacial interaction between h-BN and Si3N4 and will give a promising theoretical guidance for designing and optimizing h-BN-based ceramic composites.

Revealing the Interplay of Local Environments and Ionic Transport in Perovskite Solid Electrolytes.

Solid-state ionic conduction is significantly influenced by bottleneck sizes, which impede ion diffusion within solid lattices. Using aberration-corrected scanning transmission electron microscopy and multislice electron ptychography, we directly observed that increased La occupancy in the perovskite solid electrolyte Li0.5La0.5TiO3 correlates with reduced bottleneck sizes formed by four oxygen atoms connecting neighboring A-site cages. This correlation was also confirmed in local aperiodic regions, where smaller bottleneck sizes due to increased La occupancies affect the directionality and dimensionality of the Li+ ion conductivity. Furthermore, while prior studies have focused on averaged Li+ ion diffusion across different bottleneck areas or chemical environments, by devising a molecular dynamics (MD)-based methodology, we quantify the diffusivity of Li+ ions through specific bottleneck regions. Atomistic simulations, including nudged elastic band calculations and this MD-based methodology, revealed that larger bottleneck sizes correlate with smaller local migration barriers and higher local diffusivity. This study elucidates the relationship among local chemistry, lattice structure, and Li+ ion transport, providing insights for the design of advanced oxide solid electrolytes.

A Newly Predicted Magnetic TMB6 Monolayer for Efficient Nitrogen Fixation.

Developing electrocatalysts for the N2 reduction reaction (NRR) with high activity, high selectivity, and low cost is urgently required to enhance the NH3 yield rate. Based on first-principles calculations, we predict a series of new transition metal boride TMB6 (TM = Ti, V, Cr, Mn, Fe, and Co) monolayers and investigate their magnetoelectronic and electrocatalytic properties. The results reveal that VB6 and CoB6 favor ferromagnetic coupling, while TiB6, CrB6, MnB6, and FeB6 display antiferromagnetic ordering. Furthermore, TiB6 exhibits a high Néel temperature of 344 K and a large magnetic anisotropy energy of 614 μeV per Ti atom. Most interestingly, TiB6 and VB6 exhibit superior NRR catalytic activity with a limiting potential of -0.50 and -0.19 V, respectively, and favorable NRR selectivity over the HER. Finally, the structural stability of TMB6 monolayers has been confirmed by a set of phonon dispersion, molecular dynamics, and elastic constant calculations. Our results highlight the use of the newly designed two-dimensional (2D) TM borides as promising candidates for spintronic devices and nitrogen fixation applications.

A method for assessing the risk of rockburst based on coal-rock mechanical properties and In-Situ ground stress

With the increase in mining depth and intensity, dynamic disasters such as rockburst in mines are becoming more severe. Deep resource extraction is characterized by a high in-situ stress geological environment, closely associated with geological dynamic disasters. However, there is currently no quantitative analysis method for the correlation between the two. In this study, an elastic energy density calculation method is employed, considering the dissipative effect of the self-weight stress field on the tectonic stress field. The remaining energy, referred to as impact energy, is used to classify the risk of coal seam impact, providing a computational method for rapid assessment of impact risk before mining production. The proposed calculation method is compared with 22 mine impact engineering practices in the literature, showing accurate predictions for 21 mines. Since measuring in-situ stress and coal seam physical and mechanical properties is a preliminary work in coal seam extraction, the comprehensive analysis of these data holds significant research and practical value.

First-principles calculations of phase transition, phonon spectra, thermodynamic properties and elasticity for PuO2 polymorphs

The first principles are utilized to calculate the phase transition, phonon spectra, thermodynamic properties, and elasticity of PuO2 under varying pressures. Under the compression condition, the anticipated pressure of phase transition from Fm3‾m to Pnma is 26.7 GPa, from Pnma to Cmcm is 112.9 GPa, and from Cmcm to I4/mmm phase is 588.0 GPa. As the pressure decreases, the phase transition pressure of anticipating from Fm3‾m phase to P42/mnm phase occur at −8.6 GPa. The phonon spectra of these six structures show that all phases are dynamically stable under the selected pressure. Meanwhile, the verification results of the mechanical stability criterion show that Fm3‾m, Pnma, Cmcm and I4/mmm of PuO2 are mechanically stable, nevertheless P42/mnm is unstable in high pressure. The thermodynamic properties were then calculated to further research the patterns of variation in the coefficient of thermal expansion, bulk modulus, Gibbs free energy, and heat capacity with temperature, and these were compared with experimental data.

Unveiling half-metallic, thermoelectric and optoelectronic behavior of the new Heusler alloy RbCrZ (Z = Si, Ge): a DFT perspective

Abstract Utilizing the density functional theory (DFT) method, this study aims to predict with precision the structural, elastic, electronic, magnetic, thermoelectric, thermal, and optical properties of two recently discovered half-Heusler alloys, namely RbCrSi and RbCrGe. The exchange and correlation potential are accounted for using the generalized gradient approximation of Perdew–Burke–Ernzerhof (GGA-PBE) and the Tran–Blaha-modified Becke–Johnson exchange potential (TB-mBJ). Through structural analysis, it is observed that both RbCrSi and RbCrGe alloys exhibit energetic stability in a type-3 structure with a ferromagnetic (FM) state. Both alloys exhibit half-metallic properties and integer magnetic moments of 3 μB, following the Slater-Pauli rule. Additionally, elastic calculations confirm their mechanical stability and anisotropic ductile behavior. The quasi-harmonic Debye model (QHDM) is employed for calculating thermodynamic properties, while the BoltzTraP code, based on semi-classical Boltzmann theory (SCBT), is utilized for evaluating thermoelectric properties. Findings reveal that RbCrZ alloys (with Z = Si, Ge) exhibit high figure of merit (ZT) values nearing unity at highest temperature. Consequently, the newfound half-Heusler alloys RbCrSi and RbCrGe hold significant promise for applications in thermoelectricity and spintronic devices. This comprehensive analysis underscores the potential of these alloys in the realm of renewable energy applications.

The first-principles prediction of mechanical, electronic, elastic and thermodynamic properties of Mo2XB2 (X=Nb, Os, Ta)

The mechanical, electronic and elastic properties of Mo2XB2 (X = Nb, Os, Ta) at different pressures (0–50 GPa) were predicted using first-principles calculations. The enthalpy of formation and the elastic constant calculations show that the three transition metal borides are thermodynamically and mechanically stable. The analysis of density of state and band structure reveals that Mo2XB2 (X = Nb, Os, Ta) have metallic and covalent properties. The increase of pressure will increase the elastic modulus of Mo2XB2 (X = Nb, Os, Ta). The elastic modulus of Mo2XB2 (X = Nb, Os, Ta) are anisotropic. Furthermore, the quasi-harmonic Debye model is used to predict thermodynamic parameters at various temperatures (0–1200K) and pressures (0–50 GPa), such as heat capacity at constant pressure, heat capacity at constant volume, coefficient of thermal expansion, Debye temperature, and the Grüneisen parameter.

Pressure-induced structural variations and mechanical behavior of silicate glasses: Role of aluminum and sodium

This study investigates the effects of pressure-induced densification on the structural and mechanical properties of albite-like (12.5 % Na2O·12.5 % Al2O3·75 % SiO2) and sodium silicate (12.5 % Na2O·87.5 % SiO2) glasses using Molecular Dynamics simulations. Densification increased the coordination numbers of Al and Na, facilitated Al-O-Al clustering and formation of three-bridging oxygens, reduced T-O-T angles, and packed sodium ions in albite glass. Sodium silicate glass exhibited densification primarily through increased Na coordination, reduction of Si-O-Si angle and reduced Na-Na distances. Elastic modulus calculations revealed increased stiffness with densification due to enhanced atomic packing and glass reticulation. Uniaxial tensile tests showed densified glasses had higher ductility and strength than undensified counterparts, highlighting the positive effects of pressure-induced structural rearrangements. Hydrostatic compression tests demonstrated reversible densification under varying pressure loads, with pre-treatment conditions significantly affecting residual densification.

Proactive pricing strategies for on-street parking management with physics-informed neural networks

Effective pricing is important for on-street parking management and proactive parking pricing is an innovative strategy to achieve optimal parking utilization. For proactive parking pricing, accurately predicting parking occupancy and deriving the price elasticity of parking demand are necessary. In recent years, there have been an increasing number of studies applying big data technology for parking-occupancy prediction. However, existing research has not incorporated economic knowledge into modeling, thus preventing application of the price elasticity of parking demand. In this study, proactive pricing strategies are proposed to adjust on-street parking prices which involve a parking-occupancy prediction model and a price-optimization method. Physics-informed neural networks are employed to achieve accurate prediction of parking occupancy and calculation of parking price elasticity. An elasticity-occupancy parking-management strategy is proposed for on-street parking management which leverages parking occupancy and price elasticity to guide pricing interventions. A case study shows that the parking-occupancy prediction model can make accurate predictions and derive the price elasticity of parking demand. Proactive parking pricing enables drivers to plan their trips in advance, allowing parking occupancy within an optimal range.

Influence of a Tensile Stress on the Thermodynamics of Martensitic Transformations: Frictional Work and Stored Elastic Energy Calculations in Polycrystalline Alloys

Influence of a Tensile Stress on the Thermodynamics of Martensitic Transformations: Frictional Work and Stored Elastic Energy Calculations in Polycrystalline Alloys

Optimal Arrangements and Local Anisotropy of {100} Guinier-Preston (GP) Zones by Parametric Dislocation Dynamics (PDD) Simulations.

Stress-oriented precipitation and the resulting mechanical anisotropy have been widely studied over the decades. However, the local anisotropy of precipitates with specific orientations has been less thoroughly investigated. This study models the interaction between an edge dislocation source and {100} variants of Guinier-Preston (GP) zones in Al-Cu alloys using the parametric dislocation dynamics (PDD) method. Concentric geometrically necessary dislocation (GND) loops were employed to construct a line integral model for thin platelets. The simulations, conducted with our self-developed code based on Green's function method and Eshelby inclusion theory revealed distinct strengthening behavior along the strong and weak directions for 60° GP zones, demonstrating anisotropic strengthening from the perspective of elastic interactions. Furthermore, the optimal inclined arrangement of the GP zone array was determined through elastic energy calculations, and these results were corroborated by TEM observations.

Influence of oxygen on the hydrogen storage performance of Zr2Fe: Mechanism, diffusion pathway and DFT calculations

Zr2Fe alloy exhibits the advantages of being tritiated water-free and easy to recover in the form of reversible metal hydrides, which make it an ideal material for the trapping of hydrogen isotopes. However, its practical application is significantly limited by its susceptibility to poisoning by impurity gases such as oxygen. While significant progress has been made in understanding the effects of oxygen on hydrogen adsorption, a microscopic-level explanation of this interaction is still lacking. In this work, we employed detailed density functional theory to investigate the microscopic interaction mechanism between O2 and Zr2Fe, as well as the impact on hydrogen adsorption, addressing a gap in the current understanding. Our results reveal that O2 dissociatively adsorbs at hollow sites on the Zr2Fe surface, with oxygen atoms forming strong bonds with Zr and Fe atoms. This interaction blocks key active sites, hindering hydrogen diffusion into the alloy’s interior, as confirmed by climbing-image nudged elastic band calculations. These findings provide new insights into the inhibition mechanism caused by oxygen, offering a deeper understanding for improving the hydrogen storage performance of Zr-based alloys.

Pioneering computational insights into the structural, magnetic, and thermoelectric properties of A3XN (A=Co, Fe; X=Cu, Zn) anti-perovskites for advanced material applications

This study pioneers the utilization of computer-controlled simulations to elucidate the structural, elastic, electronic, and thermoelectric properties of A3XN anti-perovskites (A = Co, Fe; X = Cu, Zn). Starting with the development of a detailed structural model, structural optimization calculations identify the stable Pm-3m cubic phase, aligning with experimental findings. Also, these optimizations indicate the ferromagnetic phase stability of A3XN anti-perovskites, further supported by positive Curie-Weiss constants of 60 K, 80 K, and 100 K for Co₃CuN, Co₃ZnN, and Fe₃CuN, respectively. The spin-dependent electronic properties, including band structure and density of states, are explored using multiple exchange-correlation (XC) functionals—GGA, GGA + U, and GGA + mBJ. The results uphold the metallic nature of the materials, accompanied by significant spin magnetic moments. Specifically, the calculated values of magnetic moments for Co3CuN, Co3ZnN, and Fe3CuN are 5.08 μB, 3.70 μB, and 7.61 μB, respectively. Furthermore, we compute the Curie temperatures for each compound, 942.48 K for Co3CuN, 692.7 K for Co3ZnN, and 1400.41 K for Fe3CuN, which are substantially elevated, indicating robust ferromagnetic behavior that persists well above ambient conditions. Mechanical properties, including stability, deformation behavior, and ductility, are validated through elastic calculations, with various mechanical anisotropy factors examined. From an application perspective, the thermoelectric characteristics of Co3CuN, Co3ZnN, and Fe3CuN are meticulously evaluated, focusing on parameters like the Seebeck coefficient, electrical conductivity, thermal conductivity, power factor and figure of merit (zT). The analysis highlights promising power factor values of 3.0×1011(W/cm.K2), 4.0×1011(W/cm.K2), and 6.0×1011(W/cm.K2) for Co3CuN, Co3ZnN, and Fe3CuN, respectively, suggesting potential for enhanced efficiency in thermopower generation, particularly in waste heat recovery applications. Furthermore, the study provides a comprehensive analysis of the ground-state optical properties of A3XN, including the dielectric constant, photoconductivity, reflectivity, refractive index, absorption coefficient, and extinction coefficient. The reflectivity spectra demonstrate high reflectivity of 45 % across visible and ultravioletregions, suggesting suitability for applications in coatings designed to mitigate solar heating effects.

Dynamic Condensation for Efficient Band-Structure Calculations of 2D Periodic Structures

Efficient band-structure calculations are essential for understanding the mechanical behaviors of periodic materials, with significant implications in material design and phononic engineering. This paper introduces the application of the improved reduced system (IRS) technique to expedite elastic band-structure calculations. The IRS, a dynamic condensation method, partitions the unit cell degrees of freedom (DOFs) into primary and secondary sets. A strategic selection of primary DOFs retains a subset of interior DOFs alongside all exterior DOFs while truncating the remaining interior DOFs. The integration of IRS with the Craig–Bampton method for additional reduction and the imposition of Bloch boundary conditions yields a notable decrease in computational overhead. Additionally, for structures with a high number of interior DOFs, a substructuring scheme can be implemented to further enhance efficiency. This approach offers a compelling combination of accuracy and expedited computation, making it applicable across diverse periodic materials.

Impact of Lattice Strain on the Electronic and Thermoelectric Properties of CoAs3 Skutterudite Material

Using density functional theory (DFT) combined with semi‐classical Boltzmann transport theory, the electronic and thermoelectric properties of binary skutterudite CoAs3 material are investigated up to 30 GPa. Elastic properties calculations confirm the mechanical stability at 0 GPa and under varying hydrostatic pressures, with ductility influenced by pressure. To ensure dynamical stability, the phonon dispersion frequencies are computed at both 0 and 30 GPa. Electronic band structure calculations, using the GGA + TB‐mBJ approximation, indicate that CoAs3 initially exhibits a direct band gap at its equilibrium lattice constant, which shifts to become indirect under increasing pressure. To assess the impact of pressure on the thermoelectric properties of CoAs3, the Seebeck coefficient, thermal conductivities, and figure of merit (ZT) are calculated at pressures of 5, 10, 20, and 30 GPa for various temperatures (300, 600, 900, and 1200 K). These computations provide valuable insights into how varying pressures influence the material's thermoelectric performance. The optimal thermoelectric properties in CoAs3 material are achieved at 5 GPa and 1200 K for n‐doping (20 GPa and 600 K for p‐doping), with an ideal doping concentration of 1.5 × 1021 cm−3 (5.5 × 1018 cm−3). Under these conditions, the material reaches a high figure of merit (ZT) value of 0.52 for n‐doping and 0.49 for p‐doping. These findings underscore CoAs3 as a promising candidate for applications in energy harvesting and optoelectronic systems, showcasing its robust thermoelectric performance under precise pressure and temperature conditions.

Lattice dynamics and vibrational properties of scheelite-type alkali-metal perrhenates

The present work provides insight into the structural, vibrational, and elastic properties of scheelite-type alkali-metal perrhenates AReO4(A= Na, K, Rb, and Cs) via first-principles calculations. Sodium, potassium, and rubidium perrhenates are isostructural and crystallize in a tetragonal structure, whereas cesium perrhenate crystallizes in an orthorhombic structure. All the phonon frequencies and their corresponding mode assignments were estimated through the linear response method within density-functional-perturbation theory. The phonon density of states highlights the participation of the oxygen anions and both the A-type and rhenium (Re) cations in the low-frequency range. In contrast, the oxygen and Re atoms make relatively high and moderate contributions to the remaining phonon frequency spectrum. Considerable splitting of the longitudinal and traverse optic modes was observed. Elastic constants and phonon dispersion calculations confirmed the mechanical and dynamic stability of the studied AReO4compounds. A redshift was observed with the frequency of the phonons following the sequence Na→Cs. The low value calculated for the bulk modulus (ranging from 28.36 GPa to 14.15 GPa) and shear modulus indicates the perrhenates have a low resistance to deformation. The values of these moduli decrease in the order of Na→Cs, which correlates with an increase in an ionic radius of the cation. The response to pressure was found to be anisotropic. This characteristic and the ductile nature of the alkali-metal perrhenates were confirmed through elastic analysis.

A Novel Nano-Spherical Tip for Improving Precision in Elastic Modulus Measurements of Polymer Materials via Atomic Force Microscopy.

Micro-nano-scale mechanical properties are vital for engineering and biological materials. The elastic modulus is generally measured by processing the force-indentation curves obtained by atomic force microscopy (AFM). However, the measurement precision is largely affected by tip shape, tip wear, sample morphology, and the contact model. In such research, it has been found that the radius of the sharp tip increases due to wear during contact scanning, affecting elastic modulus calculations. For flat-ended tips, it is difficult to identify the contact condition, leading to inaccurate results. Our research team has invented a nano-spherical tip, obtained by implanting focused helium ions into a silicon microcantilever, causing it to expand into a silicon nanosphere. This nano-spherical tip has the advantages of sub-micro size and a smooth spherical surface. Comparative tests of the elastic modulus measurement were conducted on polytetrafluoroethylene (PTFE) and polypropylene (PP) using these three tips. Overall, the experimental results show that our nano-spherical tip with a consistent tip radius, symmetrical geometric shape, and resistance to wear and contamination can improve precision in elastic modulus measurements of polymer materials.

Stability and properties of six new Ru3Al structures: A first-principles study of mechanical, electronic, and superconducting properties

Ruthenium–aluminium (Ru–Al) alloys demonstrate excellent properties; however, the Ru3Al structure has a higher formation energy than those of other Ru–Al structures. Herein, to identify more stable Ru3Al structures, we employed the CALYPSO code and discovered six stable structures: one hexagonal structure, two monoclinic structures and three orthorhombic structures. First-principles calculations and the density functional theory were used to assess their mechanical, electrical and superconducting properties. The formation energies of these newly discovered Ru3Al structures were lower than those of previously proposed structures, confirming their thermodynamic stability. Elastic constant calculations indicated that all the structures were mechanically stable and ductile. Moreover, electronic structure analyses revealed that the structures were metallic, primarily owing to the contribution of Ru d orbitals. Phonon dispersion and density of states analyses also confirmed the dynamic stability of the structures, with low-frequency phonons contributing considerably to electron–phonon coupling. The superconducting transition temperatures (Tc) of the structures were calculated using the Allen–Dynes-modified McMillan equation. The Cmcm structure showed the highest Tc of 3.99 K, and the P2/c structure showed the lowest Tc of 1.56 K. Overall, this study identified six novel and stable Ru3Al structures with good mechanical and superconducting properties, potentially advancing the development of Ru–Al-based superconductors.

A highly efficient semi-finishing approach for polycrystalline diamond film via plasma-based anisotropic etching

Plasma anisotropic etching polishing (plasma-AEP), a non-contact polishing method, is proposed to achieve highly efficient planarization of polycrystalline diamond (PCD) films. Inductively coupled plasma, with a high concentration of reactive radicals, serves as the source of plasma-AEP. In-situ observation confirms that the planarization effect of plasma-AEP is realized through the preferential removal of the top areas of the pyramid-shaped protrusions, despite the entire surface being uniformly irradiated by the plasma. The material removal rate in plasma-AEP for PCD achieves 127 μm/min. Plasma-AEP is proven effective for PCD films with thicknesses of 0.5, 1, and 2 mm, demonstrating a generic semi-finishing approach for PCD regardless of thickness. Atomic-scale nudged elastic band calculations revealed that the energy barriers for CO and CO2 desorption from 1- and 2-coordinated C atoms are significantly lower than those for 3- and 4-coordinated ones. ReaxFF molecular dynamics simulations showed that at the top areas of the pyramid-shaped protrusions, 1- and 2-coordinated C atoms with a higher etching priority remained dominant during plasma-AEP, leading to the preferential removal of C atoms forming these protrusions. Furthermore, contact polishing was added to complete the finishing of the PCD film, followed by plasma-AEP, resulting in a nanoscale smooth surface with a roughness of 3.4 nm. Transmission electron microscopy confirmed that the crystal structures on the surface and subsurface of the PCD film were well ordered. Overall, this paper displays that plasma-AEP is a promising approach for highly efficient semi-finishing of PCD films.

A General Formulation of the Resonance Spectrum Expansion Self-Shielding Method

The resonance spectrum expansion (RSE) self-shielding method was recently proposed by Nagoya and Osaka universities as a powerful alternative to existing approaches. First investigations of the RSE at Polytechnique Montreal show that it can effectively replace the actual subgroup method used for production calculations in DRAGON5. The Japanese implementation of the RSE method is limited to a solution of the Boltzmann transport equation (BTE) with the method of characteristics. We are proposing a new implementation of the RSE method compatible with various types of solutions for the BTE, including the collision probability and the interface current methods. We based our validation study on a subset made up of eight Rowlands pin cell benchmark cases. The absorption rates obtained after self-shielding are compared with exact values obtained using an elastic slowing-down calculation where each resonance is modeled individually in the resolved energy domain. Validation of Rowlands benchmark with effective multiplication factor calculations was also conducted with respect of the SERPENT2 Monte Carlo code. It is shown that the RSE method is compatible with both advanced and legacy energy meshes and performs slightly better than the production subgroup methods actually used.