Effect Of Vacancy Concentration Research Articles

Effects of vacancy concentration on the edge dislocation motion in copper by atomic simulations

Nonequilibirum vacancy concentration widely appears in crystals under many extreme loading conditions, but receives relatively few attentions. In this work, we systematically explore the influence of a serial of different vacancy concentrations on the edge dislocation motion in copper using molecular dynamics (MD) simulations. Our result shows that the vacancy would hinder the dislocation motion, but the mechanism depends on the detailed dislocation motion regions. In thermally activated region, its influence is mainly reflected by modifying the dynamic and static threshold stresses required for edge dislocation initiation and continuous motion. In the linear region, the hindering mechanism is gradually transformed from phonon damping to vacancy pinning with the increasing vacancy concentration. In contrasts, the dislocation structure is almost unchanged under different vacancy concentrations in the non-linear region. Under high applied stress, high vacancy concentration will cause the dislocation velocity to jump back and forth between transonic and subsonic velocities more frequently. It has been attributed to the reactions between the dislocation and vacancies. The latter may result in dislocation local constriction and climbing. Moreover, a mobility equation suitable for describing edge dislocations at different non-equilibrium vacancy concentrations is proposed, which fits the MD results well. Finally, the roles of the nonequilibirum vacancy concentration on the edge dislocation motion is interpreted using the degrading elastic property and stacking fault energy.

Effect of vacancy concentration on the production selectivity of Janus In2S2X (X=Se, Te) monolayer heterojunction photocatalytic reduction of CO2

Photocatalytic reduction of CO 2 to renewable energy is considered as one of the important strategies to simultaneously solve the problems of environmental pollution and energy shortage. However, high carrier recombination probability and low product selectivity seriously affect the further development of this technique. Here, we propose a novel 2D In 2 S 2 X (X = Se, Te) Janus structure catalyst. It exhibits excellent photocatalytic performance: (a) The valence band maximum and the conduction band minimum are contributed by the bottom and top atoms, respectively, so the photogenerated electrons have a bottom-up transition direction. The intrinsic polarization makes In 2 S 2 X have a built-in electric field opposite to the electron transition direction, so it extremely promotes the separation of carriers and inhibits electrons-holes recombination. (b) More importantly, the vacancy concentration on the catalyst surface can control the selectivity of the reduction products, and CO 2 molecules are reduced to HCOOH and HCHO on the surfaces of single and double vacancies, respectively. The calculated free energies reveal that In 2 S 2 Te exhibits excellent catalytic performance for photoreduction of CO 2 on both single- and double-vacancy surfaces, indicating the great potential of In 2 S 2 Te in the field of photocatalysis. This work sheds some light on the design of novel materials and provides some insights into the regulation of desired functions through defect engineering. • A five-layers Janus In 2 S 2 X (X = Se, Te) monolayer is designed. • The built-in electric field of In 2 S 2 X promotes the separation of carriers. • Vacancy defect concentration regulates reduction product selectivity.

Vacancy dependent mechanical behaviors of high-entropy alloy

An abundance of defects would be inevitably generated during manufacturing and service in high-entropy alloys (HEAs). However, the mechanical properties of the damaged HEAs with nanoscale defects have been rarely considered. Meanwhile, an additional challenge is a dearth of the effective reliable method for an in-depth study of damaged HEAs, due to the restriction of the complicated experimental measurement. Here, the effect of zero-dimensional defect, such as vacancy, on mechanical properties in FeNiCoCrCu HEA is studied through the method combining molecular dynamics simulation with machine learning. Atomic simulation results show that the existence of vacancy clusters breaks the continuity of stacking faults and dislocations, and the high vacancy concentrations reduce the strength due to the increase of stacking fault spacing at room temperature. Compared with traditional alloys, HEAs can reduce the property reduction when vacancy exits there. In addition, the anisotropy of vacancy effect is found. The effect of vacancy on the yield strength is more obvious under [100] loading direction than that under the [110] and [111] loading direction. The discrepancy of the stair-rod partial dislocation proportion would be regarded as the primary reason for different yield strengths. The change of vacancy concentration has a significant effect on the deformation mechanism in [100] direction, which is different from that in the [110] and [111] direction. Meanwhile, the effects of vacancy concentration in combination with temperature on the yield strength and dislocation density at yield point of the FeNiCoCrCu HEA are predicted by machine learning, which is on the basis of a set of data obtained from molecular dynamics simulations. The current work provides valuable guidance for HEA design based on the viewpoint of defect regulation.

Increased Vacancy Concentrations Improve Li+ Diffusion in Solid State Battery Electrolyte Li3OCl

All solid-state batteries are a promising new technology that can replace the current Li-ion batteries. The solid inorganic electrolyte offers advances in safety, durability, and volumetric and gravimetric energy density. The anti-perovskites lithium oxychloride (Li3OCl) and the hydroxychloride (Li3−xHxOCl) are promising solid electrolytes, though more optimization is required. Performance of these lithium rich anti-perovskites can be improved through understanding the diffusion mechanism through simulation. Here, we report the first comprehensive study varying Li+ concentrations in Li3OCl using ab-initio molecular dynamics simulations. The simulations accurately capture the complex interactions between Li+ vacancies (V’), with concentrations between 0.5-2%. Analysis of discretized local diffusion events in both space and time lend insight into the effect of vacancy concentration on the diffusion mechanism and the lowering of the activation energy barrier. The results reveal the critical interplay between lattice polarization, disorder, and correlated dynamics in promoting ionic conductivity in Li3OCl.

The Effect of Vacancy Concentration on the Migration Rate of the Tilt Boundaries in Nickel: Molecular Dynamics Modeling

The Effect of Vacancy Concentration on the Migration Rate of the Tilt Boundaries in Nickel: Molecular Dynamics Modeling

Influences of Vacancy Concentration and Al Substitution on Structural, Electronic, and Elastic Properties of Nb5Si3 from First‐Principles Calculations

The effects of vacancy concentration and Al substitution on the structural, electronic, and elastic properties of Nb5Si3 are studied using first‐principles calculations. The formation energy, elastic modulus, and electronic properties of three different Nb vacancies in Nb5Si3 are discussed in detail. With the increase in vacancy concentration, the obtained shear modulus, Young's modulus, and hardness of Nb vacancy decrease, which are lower than those of pristine Nb5Si3. The bulk modulus/shear modulus (B/G) ratio increases with the increase in Nb vacancy concentration. However, these vacancies result in the transition from brittleness to ductility, and Nb5Si3 with 5% vacancy concentration exhibits ductile behavior. The calculation of electronic structure shows that these Nb vacancies change the local hybridization between Nb and Nb atoms. As the concentration increases, the position of the peak moves toward lower energy. It is predicted that vacancies can improve the ductility behavior of Nb5Si3.

First-principles study of sulfur vacancy concentration effect on the electronic structures and hydrogen evolution reaction of MoS2

Defect engineering has been widely used in experiments to modulate the electrocatalytic properties of molybdenum disulfide (MoS2). However, the effect of vacancy concentration on the vacancy distribution, electronic properties, and hydrogen evolution reaction (HER) activity remains elusive. Herein, we perform density functional theory (DFT) studies to investigate defective MoS2 with different numbers of sulfur vacancies. In the case of low S-vacancy concentration, the vacancies prefer to agglomerate rather than being dispersed, while at the higher-vacancy concentration, the combination of local point defect and clustered vacancy chain is preferred. The coupling between S-vacancies leads to decreased band gap and increased Mo–H adsorption strength with increasing vacancy concentration. The optimal HER activity is identified to occur below vacancy concentration of 12.50%. Our work provides an atomic-level understanding about the role of S-vacancies in the HER performance of MoS2, and offers useful guidelines for the design of defective MoS2 and other TMDs electrocatalysts.

Влияние концентрации вакансий на скорость миграции границ наклона в никеле: молекулярно-динамическое моделирование

The effect of vacancy concentration on the migration rate of high-angle tilt boundaries with misorientation axes <111> and <100> in nickel was studied by the method of molecular dynamics. It is shown that the dependence of the migration rate of grain boundaries on the vacancy concentration is nonmonotonic and has a maximum at a concentration of vacancies introduced at the initial stage of about 1%. With a further increase in concentration, especially above 4%, the migration rate of the considered boundaries decreased as a result of deceleration of boundaries by low-mobility vacancy clusters attached to it, which the boundary could no longer sorb, as in the case of relatively small clusters.

Atomistic relaxation process in a Ni3Al ordered phase using path probability method with vacancy mechanisms

The path probability method (PPM), which is a natural extension of the cluster variation method (CVM) to a time domain, has been employed in a relaxation process of atomic configurations in alloy systems. Although the vacancy mechanism is the main atomic migration process in an alloy system, most studies of PPM have used the spin flipping mechanism (or the direct exchange mechanism) because of the huge computational burden imposed by the vacancy mechanism. In this paper the computational problem is circumvented by treating various path variables in the PPM as cluster probabilities in the CVM, and the vacancy mechanism is explicitly taken into account in the theoretical framework. The method is employed to explore the relaxation process in a Ni3Al ordered phase within the tetrahedron approximation, and the effect of vacancy concentration is investigated.

Effects of Vacancy Concentration and Temperature on Mechanical Properties of Single-Crystal γ-TiAl Based on Molecular Dynamics Simulation

Abstract Molecular dynamics simulation is used to analyze tensile strength and elastic modulus under different temperatures and vacancy concentrations. The effects of temperature and vacancy concentration on the mechanical properties of γ-TiAl alloy are investigated. The results show that the ultimate stress, ultimate strain and elastic modulus decrease nonlinearly with increasing temperature and vacancy concentration. As the temperature increases, the plastic of material is reinforced. The influence of temperature on strength and elastic modulus is larger than that of vacancy concentration. The evolution process of vacancy could be observed clearly. Furthermore, vacancies with different concentrations develop into voids first as a function of external forces or other factors, micro cracks evolve from those voids, those micro cracks then converge to a macro crack, and fracture will finally occur. The vacancy evolution process cannot be observed clearly owing to the thermal motion of atoms at high temperature. In addition, potential energy is affected by both temperature and vacancy concentration.

Structural characterization of aluminized steel heat treated in different environments

Thermal and plasma based heat treatments of Aluminized P91 steel under different environments such as 100%O2, 100%Ar and 50%O2+50% Ar are attempted to investigate microstructural defects. Heat treatment of Al coated P91 steel involving normalizing treatment at 980°C and tempering at 750°C for 0.5h and 1.5h respectively in above mentioned environments under thermal and plasma processing conditions at 5mbar pressure was conducted. Detailed study of microstructural evaluation of the resultant diffusion coating under different environment is reported with SEM-EDS and EBSD characterization in current study. Further the vacancy concentration, CV was evaluated based on the precise combination of the changes in the bulk length and the X-ray lattice parameter from XRD data. The effect of vacancy concentration, grain size and strain on resultant coating has been presented. Presence of stable α-Al2O3 and metastable θ-Al2O3 along with FeAl was confirmed by XRD analysis in both thermal and plasma processed samples under 100%O2 and 50%O2+50%Ar environment while in Ar environment minor presence of θ-Al2O3 was observed during plasma treatment. Plasma heat treatment under 50%O2+50%Ar environment results in coating with stable α-Al2O3 followed by diffusion zone of FeAl with lowest vacancies, residual strain and area fraction of kirkendall porosity with maximum length of diffusion zone of FeAl phase for aluminized P91 steels than plasma treatment under 100% Ar environment and 100% O2.

Effect of Vacancy Concentration on Elastic and Electronic Properties of InAs and GaAs: Towards Defected Structures of Nanoobjects.

This paper pertains to elastic properties of InAs and GaAs semiconducting crystals containing various amounts of vacancies--the relevant issue in the case of nanostructured electronic materials. The linear relationship between elastic constants and point defects concentration deduced from our classical molecular dynamic and ab initio calculations, confirms that an increasing vacancy content results in a decrease of pertinent elastic parameters, namely the crystal elastic stiffness-tensor components, the effect called herein "the softening of material" for simplicity. The pseudo-potential-based approach provides us results compatible with the available experimental data, while the alternatively used empirical potentials failed to account for different kind of vacancies on the elastic properties of semiconductors. Our results provide an expanded insight into the problems of modeling of the properties of the defected InAs and GaAs crystal structures. This issue is of interest to nanoelectronics and production of nanomaterials currently.

The Study on Deposition Process and Mechanical Properties of Deposited Cu Thin Films Using Molecular Dynamics

This paper studies the deposition process and mechanical properties of Cu thin films deposited on single crystal copper substrates with various surface roughnesses by molecular dynamics (MD). In the effect of vacancy concentration (Cv) of substrate, the Young's modulus of sample decreased as the Cv of substrate increased but the adhesion force will increase as the Cv of substrate increases. The effect of substrate roughness on the peak intensity of crystal orientation has little. And the greater Cv of substrate, the surface roughness of the deposited thin film also increased. In the effect of numbers of deposited atoms, the deposited thin film thickness increases, the surface will be relatively flat and the Young's modulus will also increase. By the XRD pattern, the principal growth directions of thin film are the (220) and (200) in the early stage of growth during deposition. However, with the thickness increasing, the (111) will be the preferred orientation.

Effect of vacancy concentration on the relaxor properties of complex niobates of alkaline and alkaline-earth elements

Effect of vacancy concentration on the relaxor properties of complex niobates of alkaline and alkaline-earth elements

Vacancy-assisted arsenic diffusion and time-dependent clustering effects in silicon

We present results of kinetic lattice Monte Carlo (KLMC) simulations of substitutional arsenic diffusion in silicon mediated by lattice vacancies. Large systems are considered, with 1000 dopant atoms and long-range ab initio interactions, to the 18th nearest lattice neighbor, and the diffusivity of each defect species over time is calculated. The concentration of vacancies is greater than equilibrium concentrations in order to simulate conditions shortly after ion implantation. A previously unreported time dependence in the applicability of the pair diffusion model, even at low temperatures, is demonstrated. Additionally, long-range interactions are shown to be of critical importance in KLMC simulations; when shorter interaction ranges are considered, only clusters composed entirely of vacancies form. An increase in arsenic diffusivity for arsenic concentrations up to ${10}^{19}\phantom{\rule{0.3em}{0ex}}{\mathrm{cm}}^{\ensuremath{-}3}$ is observed, along with a decrease in arsenic diffusivity for higher arsenic concentrations, due to the formation of arsenic-dominated clusters. Finally, the effect of vacancy concentration on diffusivity and clustering is studied, and increasing vacancy concentration is found to lead to a greater number of clusters, more defects per cluster, and a greater vacancy fraction within the clusters.

Effects of vacancy concentration on the magnetic and transport properties of (La 1− xPb x) 1− y□ yMnO 3

(La 1− x Pb x ) 1− y □ y MnO 3 with x=0.05–0.5 and y=0, 0.05, 0.1 (where □ is a vacancy) was studied to evaluate the effects of A-site vacancies on the physical properties. In this system manganese perovskites form with tolerance factors close to 1 and low A-site cation size mismatch due to similarities in the effective ionic radii of La 3+ and Pb 2+. Increasing vacancy concentration indicates no significant effect on the lattice parameters or volume. However, the vacancies introduce a greater A-site cation size mismatch, which leads to a lowering of the ferromagnetic and metal–insulator transition temperatures, although the transitions are not broadened with increasing vacancy content. Due to the vacancies a distribution of Mn–O–Mn angles and Mn–O distances are created, and long range order in (La 1− x Pb x ) 1− y □ y MnO 3 appears to be determined by Mn–O–Mn angles and Mn–O distances which most distort from 180° and are the longest, respectively, in the structure.

The electronic and positronic structure of defects in materials

We have employed a first-principles supercell methodology based on the charge selfconsistent KKR band theory framework in order to investigate the electronic and positronic structure of defected systems. Judicious use of the KKR-CPA disordered alloy theory in conjunction with the supercell calculations allows us to gain insight into effects of vacancy concentration, of electronic relaxation, and of electron-positron correlation on the positron state. We illustrate our approach by considering examples of a monovacancy in Al and Si, a single P impurity in Si, and the As-vacancy complex in Si.

Computer Simulation of Vacancy Segregation at Antiphase Domain Boundaries During Coarsening

AbstractA computer simulation technique based on the Master Equation Method (MEM) is developed for modeling the spatial distribution of vacancies during ordering and subsequent domain coalescence and coarsening. A vacancy mechanism is assumed for the atomic diffusion and the single-site approximation is employed. It is demonstrated that vacancies strongly segregate into the antiphase domain boundaries (APBs) during coarsening, resulting in the vacancy concentration at APBs more than an order of magnitude higher than that inside the ordered domains. As the antiphase domains coarsen, the vacancy concentration at the APBs continues to increase and its spatial s segregation profile moves accompanying the APB migration. The effect of vacancy concentration on the antiphase domain coarsening kinetics is discussed.

Refractive indices of the condensed rare gases, argon, krypton and xenon

A recently designed refractometer employing the phenomenon of total internal reflection is used to measure the refractive indices of the condensed phases of the rare gases argon, krypton and xenon in the temperature ranges 35-90K, 60-117K and 30-178K, respectively. The values obtained for argon and xenon are in good agreement with those obtained by the method of minimum deviation, but values for krypton obtained by the two methods differ by more than the combined experimental error. This difference does not appear to be due to impurities. Experimental values of the refractive indices have been used to compute values of the Lorentz-Lorenz function for comparison with predictions arising from the theoretical models of C.J.F. Bottcher and of H. Block and S.M. Walker and to obtain revised values of the parameters for the theoretical treatment of S. Doniach and R. Huggins. The effect of vacancy concentration on density and hence on the Lorentz-Lorenz function is discussed.