Search

Kinetic Monte Carlo (KMC) simulations have been used for electron beam physical vapor deposition (EB‐PVD) of ZrO2 coatings, with the critical potential function fitted by full first‐principles calculations in the framework of density functional theory, emphasizing the effect of critical processing parameters, for example, the substrate temperature (600–1150 K), deposition rate (0.03–7.5 μm/min), and initial kinetic energy (0–0.5 eV). Here, the interaction between ZrO2 particles is described by coarse grain (CG) model with a numerical non‐bonded potential developed by multi‐iterative boltzmann inversion (multi‐IBI). Overall, the calculated energy barrier by the nudged elastic band (NEB) shows the internal diffusion (3.29–4.80 eV) requires more energy than the surface diffusion (2.90–3.42 eV), because of fewer surrounding particles in the latter. Moreover, the energy barrier of Line Jump is smaller than that of Schwoebel Jump, contributing to the columnar grains rather than a dense coating. Of importance, the simulated morphologies of ZrO2 coatings are well consistent to experiments, with a weaker effect from the substrate temperature, initial kinetic energy to deposition rate. Furthermore, the porosity can be effectively reduced by increasing the temperature and initial kinetic energy, however, with a slight increase when increasing the deposition rate. [ABSTRACT FROM AUTHOR]

[Display omitted] • A machine learning potential is developed to perform MD simulation with DFT accuracy. • The mechanical properties of BZO with various Y-doping concentrations were compared. • The mechanical properties of BZY with various levels of hydration were compared. • The mechanical properties of BZY and hydrated BZY were compared. The hydration reaction leads to non-uniform stresses and strains inside solid oxide electrolytes, which seriously affects the mechanical properties of the material. Machine learning (ML) molecular dynamics (MD) provides an excellent means to investigate the effects of hydration on the structural and mechanical properties of electrolytes. In this paper, we develop an excellent ML potential with the accuracy of near first principles calculations and the efficiency of classical MD simulations to study the doping and hydration of BaZrO 3 (BZO) materials. The lattice constants, elastic constants, thermal expansion coefficients (TEC) and melting point of BZO and the enthalpy of hydration of Y doped BaZrO 3 (BZY) were calculated, and the results agree with the density functional theory (DFT) reference data, validating the accuracy of the ML potential. The study of the mechanical properties of BZY after the occurrence of the hydration reaction reveals that the Young's modulus and strength decrease significantly with the increase of the Y doping concentration, and the main reason for this decrease is the creation of oxygen vacancies by the doping process, which reduce the number of chemical bonds. The increase in hydration level also causes a decrease in the Young's modulus and strength, which is mainly attributed to the chemical expansion and weakening of the chemical bonds caused by protonic defects. Finally, the changes in Young's modulus and strength before and after hydration was also found to be only slightly different, indicating that the bond-strengthening effect induced by the filling of oxygen vacancies is compensated mainly by the bond-weakening due to protonic defects. The research results can contribute to understanding material design rules to rationalize the chemical expansion to optimize the chemical mechanical response of oxide ceramics, ultimately developing more stable proton conductors for proton based solid oxide fuel cells and electrolytic cells. [ABSTRACT FROM AUTHOR]

Summary: Gadolinia‐doped ceria (GDC), as an electrolyte of solid oxide fuel cells, reduces its mechanical property when exposed to reducing conditions. In this paper, the anisotropic mechanical behavior of non‐stoichiometric GDC solid electrolytes is investigated by using the molecular dynamics (MD) method. It is found that the oxygen vacancies whether from doping Gd3+ ions or generating Ce3+ ions by reduction have a serious impact on the mechanical properties such as phase transformation and fracture strength. The defect‐dependent tensile strength is observed to be consistent with reported experimental measurements. Moreover, increasing temperature reduces the fracture strength. The influence of temperature on the critical nucleation stress and the fluorite phase strength is further analyzed. Beyond that, GDC undergoes volumetric expansion due to non‐stoichiometric effects. The linear chemical strain and coefficient of compositional expansion (CCE) are calculated and compared with the experimental results. [ABSTRACT FROM AUTHOR]

The complex operating environment severely tests the mechanical stability of the electrolyte material BaZrO 3 (BZO), which affects the performance of solid oxide fuel cells(SOFCs). Molecular dynamics (MD) simulation provides an efficient method to research the mechanical behavior of nanocrystalline materials. In the interest of researching the mechanical behavior of BZO materials utilizing a machine learning (ML) MD approach, this article has established the most effective ML potential with DFT reliability. By contrasting the lattice constants and elastic constants with the DFT data, the precision of the potential was confirmed. By simulating the uniaxial tensile mechanical behavior of the BZO models without crack and with a central crack in the crystal orientation of [100] and [110], we found that the BZO material has a significant anisotropic property. In the crack-free model, the BZO crack propagation mode in the [100] crystal orientation is a shear fracture. The central microcrack tilts downward and expands symmetrically in the [110] crystal-oriented BZO model. When the initial structure with a central crack, the fracture mode changes significantly, and in both crystal orientations, the crack fracture along the Ba O plane, the crack expands horizontally in the BZO model in the [100] crystal orientation and the crack expands zigzag in the BZO model in the [110] crystal orientation. The calculations of fracture strength, critical energy release rate, and fracture toughness show that the [110] crystal-oriented BZO has a stronger resistance to fracture than the [100] crystal-oriented BZO model. • A machine-learning potential is developed to perform MD calculations with DFT accuracy. • Fracture mechanical behavior of BaZrO 3 with and without central cracking was compared for different crystal orientations. • Fracture parameters were calculated using ML potentials to compare fracture resistance of different BaZrO3 structures. [ABSTRACT FROM AUTHOR]

Abstract In this paper, a new interionic potential is derived for silver iodide (AgI) via the Chen-Möbius lattice inversion and ab initio calculation. The accuracy of the proposed potential is checked by comparing the molecular dynamics simulation results on the static properties, structural stability, disordered states, mean-squared displacement and phase transition of AgI with experimental data. The simulation results are consistent with experimental data and density functional theory (DFT) calculations, indicating that the proposed interionic potential is valid over a wide range of interionic separations and applicable for describing the major properties of AgI. Highlights • We derive a new interionic potential for AgI via the Chen-Möbius lattice inversion and DFT calculations. • The accuracy of the proposed potential is checked by comparing the MD simulation results with experimental and DFT data. • The potential developed in this work is more favorable in describing several properties than former potential. [ABSTRACT FROM AUTHOR]

Molecular dynamics simulations is used to investigate the mechanical properties of three‐dimensional (3D) graphene under uniaxial tensile loading. The results show that the tensile deformation of 3D graphene exhibits size dependence along both armchair and zigzag directions. By analyzing the atomic von Mises stress and structural evolution, compared to the 3D graphene with smaller in‐plane cell size, the larger 3D graphene exhibits two typical deformation events, i.e., transverse structural shrinkage and axial elastic deformation. The fracture stress of 3D graphene is much smaller than that of 2D graphene because of its porous structure. However, the fracture strain of 3D graphene is larger than that of 2D graphene due to the larger transverse structural shrinkage along both armchair and zigzag directions. Effects of temperature, strain rate, and thickness of 3D graphene on the tensile behavior is investigated. The simulation results indicate that the fracture stress and the fracture strain decrease with increasing temperature and with decreasing strain rate. However, the fracture stress and the fracture strain is not dependent on the thickness of 3D graphene. The results in this paper suggest that 3D graphene with higher stretchability tunable by in‐plane cell size can be promising multifunctional materials for many engineering applications. [ABSTRACT FROM AUTHOR]

The mechanical properties of two-dimensional (2D) interlinked carbon nanotube (CNT) network are investigated using ab initio calculation and molecular dynamics simulations (MD) with Reaxff force field. The simulation results show that bulk 2D interlinked CNT network has good mechanical properties along the axial direction which can be comparable to that of single-walled CNT and graphene, but has better ductility along the radial direction than single-walled CNT and graphene. In addition, the mechanical properties of 2D interlinked CNT network ribbon along the radial direction depend strongly on the size of the ribbon. The Young's modulus and Poisson's ratio decrease as the size increases while the fracture strain increases with the size increasing. By analyzing the atomic structural (both bond length and atomic von Mises stress) evolution of the ribbons, the mechanism of a brittle-to-ductile transition is revealed. The exploration of the mechanical properties of the 2D interlinked CNT network paves the way for application of the relevant devices that can benefit from the high Young's modulus, high tensile strength, and good ductility. [ABSTRACT FROM AUTHOR]

Graphyne, a two-dimensional planar carbon allotrope and consisting of sp and sp 2 carbon atoms, receives great attention in a wide community of scientists and engineers beyond graphene. Herewith we investigate the thermal transport property of graphyne and graphyne nanoribbons by performing nonequilibrium molecular dynamics simulation. Our simulations reveal abnormal thermal transport in graphyne that exhibits a low thermal conductivity (as low as 8 W/mK at room temperature), which is two to three orders of magnitude lower as compared to graphene. Detailed lattice dynamic calculations and phonon polarization analysis suggest that, the intrinsically low thermal conductivity of graphyne originates from the localization and the domination of the low frequency in-plan longitudinal modes to the acetylenic linkages and the large lattice vibration mismatch between the linkages and the hexagonal rings, which induces inefficient energy transfer between the soft phonon modes in the linkages and the stiffer vibrational modes in the hexagonal rings. We also illustrated an intriguing width dependent thermal conductivity of graphyne nanoribbons, which is fundamentally different from that of graphene nanoribbons and stems from the surface dominated phonon modes presented in the graphyne edge. Our simulations provide a detailed physical picture of thermal transport in graphyne and could offer useful guidance for engineering the thermal transport properties of graphyne for applications of graphyne related devices such as thermoelectrics. [ABSTRACT FROM AUTHOR]

Proton transport in perovskite oxides (ABO 3) is a complex dynamical process involving hydroxide ion rotation and proton transfer. Combining ab initio molecular dynamics (AIMD) and machine-learning molecular dynamics (MLMD) simulations of proton dynamics in Y-doped BaZrO 3 perovskite oxide, we systematically illustrate the anomalous characteristics of proton motion. At short times, proton performs superdiffusion through the O H wag and proton transfer. At intermediate times, the larger rotation angle results in the larger plateau value. At longer times, proton diffusion first becomes subdiffusive due to the hydroxide ion rotations then gradually turns to normal diffusion. A theoretical model is also offered to quantitatively describe this abnormal proton diffusion. In all, this work provides a more complete understanding of proton dynamics in perovskite oxides. • A machine-learning potential is developed to perform MD simulations with DFT accuracy. • The anomalous characteristics of proton motion in Y-doped BaZrO 3 are systematically illustrated at different time intervals. • A theoretical model is proposed to quantitatively describe the abnormal proton diffusion in Y-doped BaZrO 3. [ABSTRACT FROM AUTHOR]

The mechanical properties of silicene are investigated using ab initio calculation and molecular dynamics simulations with different empirical potentials. The simulation results show that the calculated Young's modulus of bulk silicene with EDIP model is consistent with the ab initio calculations. The chirality has a significant effect on the critical strain and stress of bulk silicene under uniaxial tension. In addition, the Young's modulus depends strongly on the chirality and size of the silicene nanoribbon due to the edge effects. The fracture process of a silicene nanoribbon is also studied. [ABSTRACT FROM AUTHOR]

Abstract: Molecular dynamics simulations are used to investigate the mechanical properties of a silicon nanofilm covered with a defective graphene. Our results show that graphene not only enhances the mechanical properties of a silicon nanofilm but also unifies the mechanical properties of the ultrathin silicon nanofilms among different crystal orientations. The Young''s modulus and critical stress of the silicon nanofilm along four crystal orientations covered with graphene decrease as the thickness of the silicon nanofilm increases. In addition, we study the effects of monoatomic vacancies and Stone–Wales (SW) defects with various concentrations on the mechanical properties of a silicon nanofilm covered with defective graphene. The results show that Young''s modulus reduces linearly for monoatomic vacancies and a relatively smaller dependence is observed on SW defects, while the critical stress is more sensitive to the presence of both types of defects. The results in this paper demonstrate the significance of graphene in enhancing the mechanical properties of the silicon nanofilm. [Copyright &y& Elsevier]

Nonequilibrium molecular dynamics (NEMD) is used to investigate the thermal-transport properties of a silicon nanofilm covered with graphene (Gr/Si/Gr nanofilm). The investigation results demonstrate that graphene can enhance the thermal-transport properties and weaken the ballistic characteristics of silicon nanofilm. Under the action of a small strain, the thermal conductivity decreases with the growth of tensile and compressive strain, respectively. In addition, the higher-frequency phonons in graphene give more contributions to the variation of thermal conductivity of Gr/Si/Gr nanofilm under strain. The thermal conductivity of Gr/Si/Gr nanofilm increases linearly with the increase of temperature in the lower-temperature regime due to the quantum effect, and begins to clearly decrease when the temperature exceeds a definite value. [ABSTRACT FROM AUTHOR]

Abstract: Molecular dynamics simulations are used to investigate the mechanical properties of a silicon nanofilm covered with graphene. Our results show that graphene can enhance the mechanical properties of a silicon nanofilm. The Young’s modulus of the silicon structure covered with graphene decreases as the thickness of the silicon nanofilm increases. We also investigate the fracture process of the silicon structure covered with graphene. The results in this paper suggest that silicon structures covered with graphene open up opportunities for design of micro and nanoelectromechanical systems. [Copyright &y& Elsevier]

Abstract: The nanomechanical properties of Si/a-Si core–shell NWs are investigated using molecular dynamics simulations with EDIP model. Under uniaxial compressive and tensile loading, the computed Young’s modulus increases as the radius of crystalline core increases and decreases as the thickness of amorphous shell increases. Whereas the critical strains are found to be independent of the size of crystalline cores and amorphous shells. For the nonaxial torsional and bending strains, both torsional stiffness and bending stiffness increase as the thickness of amorphous shell increases and also as the radius of crystalline core increases. In addition, the critical torsion angle rapidly decreases as the thickness of amorphous shells increases and also as the radius of crystalline core increases. However, the critical bending angles are independent of the size of crystalline cores and amorphous shells. These results show that the amorphous shell has significant effects on the mechanical properties of Si/a-Si core–shell NWs under external loadings. [Copyright &y& Elsevier]

Abstract: Molecular dynamics simulations are performed to investigate the interaction between 60° shuffle dislocation and tetrainterstitial (I 4) cluster in silicon, using Stillinger–Weber (SW) potential to calculate the interatomic forces. Based on Parrinello–Rahman method, shear stress is exerted on the model to move the dislocation. Simulation results show that the I 4 cluster can bend the dislocation line and delay the dislocation movement. During the course of intersection the dislocation line sections relatively far away from the I 4 cluster accelerate first, and then decelerate. The critical shear stress unpinning the 60° dislocation from the I 4 cluster decreases as the temperature increases in the models. [Copyright &y& Elsevier]

Abstract: Molecular dynamics simulations with Stillinger–Weber potential are used to study the buckling behavior of single-crystalline silicon nanowires under uniaxial compression. Nanowires with axial orientations along the [100], [110], [111], and [112] crystallographic directions, which correspond to experimentally synthesized nanowires, are studied. The effects of simulation temperature, strain rate, and wire length on the buckling behavior are investigated. The simulation results indicate that critical load clearly decreases with increasing temperature and with decreasing strain rate. Additionally, the present results show that the critical load decreases with the increase of wire length, which is in agreement with the Euler theory. [Copyright &y& Elsevier]

Abstract: The tensile and melting behaviours of single crystalline silicon nanowires (SiNWs) are studied using molecular dynamics simulations. The atomic interactions are described using the Stillinger–Weber potential. The tensile test results show that the tensile behaviour of the SiNWs is strongly dependent on the simulation temperature, strain rate, and diameter of the nanowires. The critical load clearly decreases with increasing temperature and with decreasing strain rate, and increases with increasing diameter. Additionally, the melting test results demonstrate that the melting temperature of the SiNWs decreases with decreasing diameter, due to the increase in surface energy. The structural transition of SiNWs with an increasing temperature is also studied. [Copyright &y& Elsevier]

Gadolinia-doped ceria (GDC) is one of widely used electrolyte materials for solid oxide fuel cells (SOFCs) due to its high ionic conductivity. In this paper, we report the anisotropic mechanical behavior of GDC solid electrolytes under electromechanical coupling loading by molecular dynamics (MD) simulation. For pure CeO 2 , it is found that low electric field merely reduces the fracture strength while high electric field directly changes phase transformation behavior in the [100] and [110] crystal orientations. In the [111] crystal orientation, the increase of electric field lead to the synchronous elevation of fracture stress by weakening the electrostatic repulsion between adjacent oxygen ions. And the doping concentration and temperature are considered to investigate the fracture behavior with electric field loading. Moreover, significant improvement of electrolyte conductivity is obtained by loading electric field on GDC. This finding might be able to provide a reasonable insight to reduce operating temperature of SOFC system. [ABSTRACT FROM AUTHOR]

Abstract: The thermal transport properties of single-crystalline nanowires (carbon nanowires (CNWs) and silicon nanowires (SiNWs)) covered with amorphous silicon shell are investigated by non-equilibrium molecular dynamics (NEMD). The thermal conductivity of SiNWs covered with amorphous silicon shell (Si/a-Si core–shell NWs) is obviously lower than that of single-crystalline SiNWs and it keeps approximately constant when the temperature exceeds a definite value for the diffusion properties of amorphous shell. It is quite different from that of single-crystalline SiNWs whose thermal conductivity decreases significantly for relatively higher temperature. Compared to single-crystalline SiNWs, Si/a-Si core–shell NWs express stronger non-propagation, diffusion thermal transport properties. The thermal transport properties of CNWs covered with amorphous silicon shell (C/a-Si core–shell NWs) are essentially similar to that of Si/a-Si core–shell NWs. It expresses stronger non-propagation, diffusion thermal transport properties and its thermal conductivity increases very little with the growth of length. However, its diffusion characteristics are weaker than that of Si/a-Si core–shell NWs. Generally speaking, the amorphous shell and amorphous/crystalline interface play a negative role to the thermal conductivities and an enhance role to the diffusion characteristics of single-crystalline nanowires, however, their degree of effect on different single-crystalline nanomaterials is different. [Copyright &y& Elsevier]