Search

The paper investigates the role of solid solution strengthening on the shock wave structure and Hugoniot elastic limit (HEL) in [111] copper crystals by molecular dynamics. Cu–Ni, Cu–Zn, Cu–Ag, and Cu–Al solid solutions are chosen to cover the range of atomic size misfit parameters for the solute atoms. The results show that in crystals with dislocations, the HEL decays slower with an increase in the misfit parameter of the solute, resulting in higher HEL values at a certain shock propagation distance. The Cu–Al solid solutions with the largest misfit parameter exhibit the largest deceleration of HEL decay. When the concentration of Al atoms increases to 20 at. %, the HEL almost does not change with shock propagation distance and a plateau shape of the elastic precursor is observed, as in the case of perfect crystals. In solid solutions without dislocations, the elastic precursor forms at lower velocities compared with perfect copper crystals, except for the Cu–20 at. % Ni solid solution. The HEL values increase with increasing misfit parameters and may take values lower than that for pure copper. These results show that the formation of the elastic precursor is facilitated by the presence of solid solution atoms, but the HEL magnitude and decay exponent are related to dislocation mobility in [111] copper crystals. [ABSTRACT FROM AUTHOR]

This work investigates the influence of couple stresses on intrinsic and extrinsic dislocations within three-dimensional heterogeneous multilayered structures. The materials consist of orthotropic and dissimilar layers with different elastic properties, incorporating the microstructural lengths from a special version of the anisotropic couple-stress elasticity. Double Fourier series expansions are used to describe extended displacements and tractions, considering rotation and couple-stress components and accounting for arbitrary displacement and rotation discontinuities associated with dislocation and disclination loops as well as periodic dislocation and disclination networks at semi-coherent interfaces. The dual-variable and position technique is used to recursively determine the field responses at any point in the multilayered laminate. The application examples focus on dislocation problems with couple stresses, revealing the effects of the core-spreading dislocation technique, free surfaces, anisotropic elasticity, and couple stresses on the field solutions. The analysis also uncovers pressure and von Mises stress amplitudes, non-zero rotation, and non-symmetric stress profiles due to couple stresses in copper/niobium bimaterials. Changes in the sign and magnitude of the Peach-Koehler forces are observed when couple stresses are introduced, which deviate from the classical theory of dislocations. The investigation finds a significant 29% reduction in energy per unit area at a semi-coherent interface between copper and niobium influenced by couple stresses. These results deepen our understanding of how couple stresses affect dislocation behavior in multilayered materials, and provide prospects for future discrete dislocation and disclination dynamics simulations with engineering applications in various nano- and micro-structured materials. • Novel solutions for dislocation and disclination loops in anisotropic composites. • The misfit dislocation network with couple stress is considered. • Solutions are provided by means of double Fourier series expansions. • Couple-stresses lead to a 29% reduction in energy at a semi-coherent Cu/Nb interface. [ABSTRACT FROM AUTHOR]

It is demonstrated that high‐resolution energy‐dispersive X‐ray fluorescence mapping devices based on a micro‐focused beam are not restricted to high‐speed analyses of element distributions or to the detection of different grains, twins and subgrains in crystalline materials but can also be used for the detection of dislocations in high‐quality single crystals. Si single crystals with low dislocation densities were selected as model materials to visualize the position of dislocations by the spatially resolved measurement of Bragg‐peak intensity fluctuations. These originate from the most distorted planes caused by the stress fields of dislocations. The results obtained by this approach are compared with laboratory‐based Lang X‐ray topographs. The presented methodology yields comparable results and it is of particular interest in the field of crystal growth, where fast chemical and microstructural characterization feedback loops are indispensable for short and efficient development times. The beam divergence was reduced via an aperture management system to facilitate the visualization of dislocations for virtually as‐grown, non‐polished and non‐planar samples with a very pronounced surface profile. [ABSTRACT FROM AUTHOR]

In recent years, SiC single crystal growth technology has been developed toward larger size and thickness to reduce the cost of SiC-based power devices. Resistance heating has gradually become a hot spot for research because the crystals grown by the induction heating display the disadvantages of high stress and defect density. In this paper, the design of resistance heaters for SiC crystal growth was thoroughly investigated via numerical simulation. A simulation of the thermal field generated by different resistive heater arrangements was performed. The stress and dislocation distribution in crystals under different growth conditions were studied. Based on the comprehensive requirements of a small radial temperature gradient and a large growth rate, the arrangement and length of the resistance heater were proposed. This study would serve as a useful guidance for the study of SiC growth by resistive heating. [ABSTRACT FROM AUTHOR]

The orientation-dependent mechanical behaviors of metallic alloys are governed by deformation mechanisms, but the underlying physics remain to be explored. In this work, the mechanical responses along different orientations and behind the mechanisms of BCC-Fe are investigated by performing molecular dynamic simulations. It is found that the mechanical properties of BCC-Fe exhibit apparent anisotropic characteristics. The <100>-oriented BCC-Fe presents a Young's modulus of E = 147.56 GPa, a strength of σy = 10.15 GPa, and a plastic strain of εy = 0.084 at the yield point, whereas the <111> orientation presents E = 244.84 GPa, σy = 27.57 GPa, and εy = 0.21. Based on classical dislocation theory, the reasons for such orientation-dependent mechanical behaviors are analyzed from the perspective of thermo-kinetic synergy upon deformation. It turns out that the anisotropic mechanical responses of BCC-Fe are associated with the magnitude of the thermodynamic driving force (ΔG) and kinetic energy barrier (Q) for dislocation motion, which dominate the corresponding deformation mechanism. Compared with the low ΔG (6.395 GPa) and high Q (11.95 KJ/mol) of the <100>-oriented BCC-Fe dominated by deformation twinning, the <111> orientation governed by dislocation slip presents a high ΔG (17.37 GPa) and low Q (6.45 KJ/mol). Accordingly, the orientation-dependent deformation behaviors of BCC-Fe are derived from the thermo-kinetic synergy for dislocation motion. [ABSTRACT FROM AUTHOR]

The main purpose of the paper is obtaining the analytical results for beta fractional Caudrey–Dodd–Gibbon equation which is used to resolve complex problems in fluid dynamics, chemical kinetics, plasma physics, quantum field theory, crystal dislocations, and nonlinear optics by using auxiliary method. Beta derivative is a useful fractional operator due to satisfying basic properties of integer order derivative and also, allows us using chain rule and wave transform to turn nonlinear fractional partial differential equations into integer order ordinary differential equations. By the way many analytical methods can be applied to these equations. In order to understand the physical features of the solutions, 3D and 2D graphical illustrations are given. Finally, authors expect that the obtained solutions may give a deep insight for the explanation of physical phenomena in the fluid dynamics, chemical kinetics, plasma physics, quantum field theory, crystal dislocations, and nonlinear optics. [ABSTRACT FROM AUTHOR]

Oxygen vacancies (VOs) and their distribution can affect oxides' properties from various aspects. In this work, we present a dislocation-related surface-layer effect in single crystal SrTiO3 (STO). Our results from the first principles calculations based on density functional theory along with our experimental research based on angle-resolved x-ray photoelectron spectroscopy indicate that, in contrast with bulk STO where VOs tend to cluster in a line, as depth increases from surface region, the concentration of VOs increases first, reaches a maximum value, and then decreases to a saturation value. This effect was argued to be the combinative result of the oxygen-vacancy diffusion along the dislocation lines and the ambient oxygen-atom incorporation into the crystal. [ABSTRACT FROM AUTHOR]

Basal plane dislocations (BPDs) in 4H-SiC are the main reason for the degradation of bipolar devices. In the experiment, the distribution of 4-fold symmetry BPDs is observed in the etch pit density of the 4H-SiC wafer, which is inconsistent with the phenomenon of the distribution of 6-fold symmetry BPDs because of the hexagonal structure of 4H-SiC. To explain the distribution of 4-fold symmetry BPDs in the grown crystal, 3D modeling of BPDs in 4H-SiC crystals grown by the PVT method has been performed. The results show that the adoption of 4-degree off-axis seed crystals that are widely used in the industry caused the distribution of 4-fold symmetry BPDs. Moreover, the distribution of BPDs is 6-fold symmetry in on-axis grown 4H-SiC single crystals; with the increase of the off-angle, the distribution of BPDs gradually changes from 6-fold to 4-fold symmetry, and the maximum value of the BPD density is at the periphery. In the end, the strategy of growing 4H-SiC crystals with large-size seed crystals has been proposed to reduce the BPD density in the wafer and improve the quality of the substrate. The calculation results shows that the use of 220 mm seed crystals can reduce the BPD density by 15% compared with 200 mm seed crystals. [ABSTRACT FROM AUTHOR]

To study the formation of silicides, dislocation-free ingots of single-crystalline silicon with a diameter of 65÷110 mm, grown by the Czochralski method, were used. When studying such silicon samples using electron microscopy, small-angle scattering of CO2 laser radiation, three types of defects were identified: swirl defects, impurity micro inclusions and impurity clouds. It has been shown that silicide inclusions with sizes of 8-20 μm are formed in the near-surface layer of doped silicon, and they decrease linearly deeper into the crystal. The electrical parameters of semiconductor chromium silicide were determined: resistivity 1800 μOhm·cm, thermopower coefficient 180 μV/k, Hall constant 1.2·10-2 cm3/Kl, hole concentration 6·1019 cm-3, charge carrier mobility 18.6 cm2/V·s, band gap (0.29±0.02) еV. [ABSTRACT FROM AUTHOR]

The article examines the influence of structural defects, in particular dislocations, on the electrical and photovoltaic properties of silicon four-quadrant p-i-n photodiodes. It was established that growth defects and defects formed during mechanical processing of plates can cross the entire substrate and deteriorate the parameters of photodiodes. This phenomenon is particularly negative due to the placement of defects in the space charge region. In this case, due to the presence of recombination centers in the space charge region, the life time of minor charge carriers decreases and the dark current and responsivity of photodiodes deteriorate. Often, the placement of defects is uneven, which provokes unevenness of parameters on responsive elements. It was also seen that the dislocation lines crossing the responsive elements and the guard ring worsen the insulation resistance of the specified active elements. A method of determining the final resistivity of silicon and the diffusion length of minor charge carriers by studying the pulse shape of the output signal is proposed. [ABSTRACT FROM AUTHOR]

Multi-principal element alloys (MPEAs) exhibit outstanding strength attributed to the complex dislocation dynamics as compared to conventional alloys. Here, we develop an atomic-lattice-distortion-dependent discrete dislocation dynamics framework consisted of random field theory and phenomenological dislocation model to investigate the fundamental deformation mechanism underlying massive dislocation motions in body-centered cubic MPEA. Amazingly, the turbulence of dislocation speed is identified in light of strong heterogeneous lattice strain field caused by short-range ordering. Importantly, the vortex from dislocation flow turbulence not only acts as an effective source to initiate dislocation multiplication but also induces the strong local pinning trap to block dislocation movement, thus breaking the strength-ductility trade-off. [ABSTRACT FROM AUTHOR]

Calcium fluoride (CaF 2) ionic crystals have been observed to be sensitive to humid environments during ultra-precision machining, but further discussion about detailed mechanisms of the corresponding water-induced mechanical behaviors is still lacking. This work aims to perform a systematic investigation to understand the effect of water on the deformation and correlated plastic enhancement of CaF 2 under indentation. Micro-indentation experiments were employed to observe different mechanical responses including the pop-in behavior and surface pile-up to identify the water-enhanced plasticity of CaF 2 preliminarily. Then, atomic simulations were performed to reproduce the indentation process and confirm the close relationship between the indentation behaviors and water. The dislocation activities and crystal slip of both simulations with and without water were captured to analyze the plastic flow induced by hydration. Furthermore, Raman spectroscopy measurement was also adopted in this study to explain the corresponding enhancing mechanisms of plastic behaviors from the perspective of surface effect. • Micro-indentation tests confirm the water-enhanced plasticity of CaF 2. • MD simulations explain the enhanced plasticity from the view of plastic flow. • The deformation mechanisms are uncovered by theoretical analysis. • Water enhances plasticity by pre-stressing and reducing surface effects. • Results of Raman tests further demonstrate the water-induced prestressing. [ABSTRACT FROM AUTHOR]

A new set of boundary conditions is proposed for molecular simulations of isolated elastic defects such as dislocations and cracks. The case study of the ⟨ 111 ⟩ screw dislocation in body centered cubic (bcc) tungsten, modeled via a phenomenological, n-body cohesion functional, serves validating the new boundary conditions by computing structural properties of this defect and comparing these with results from the literature. Lowest energy configurations of the dislocated crystal have been obtained by molecular statics incorporating the new boundary conditions. The associated displacement and energy landscapes reveal conformal to the predictions of the elastic theory for a screw dislocation embedded in an infinitely extended crystal. In particular, no energy gradients and positional mismatch of atoms are found at the terminations of the computational box, validating thereby the new boundary conditions. Furthermore, it is shown that the structure, the spatial extension, and the excess energy of the two possible core polarizations of this dislocation compare consistently with existing findings for this and other bcc metals. Close to the dislocation line, energy minimization triggers the emergence of anelastic edge displacements extending over distances unexpectedly much larger than the dislocation core radius. Therefore, the conclusion is reached that in molecular simulations, the transverse to the dislocation line dimensions of the atomistic model should be taken considerably larger than it is accustomed. Perspectives opened by the present work are briefly discussed. [ABSTRACT FROM AUTHOR]

The paper considers the development and numerical implementation of a two-dimensional discrete dislocation model to describe the inelastic deformation of a hexagonal close-packed (HCP) single crystal, taking into account long-range and short-range dislocation interactions. The analytical results are obtained for image fields using the Fourier series for cases of dislocation approaching the crystal boundaries. The model adequacy tests are carried out, and the evolution of the dislocation structure is illustrated with the gradual inclusion of the mechanisms of dislocation annihilation, dislocation pinning at obstacles, and dislocation nucleation by the Frank-Read sources. [ABSTRACT FROM AUTHOR]

Impact of carbon impurities on the electrical properties of lightly doped n-type GaN [electron concentration ∼(1 – 2) × 10 15 cm − 3 at room temperature] was investigated using temperature-dependent Hall effect measurements. GaN crystals with a threading dislocation density of (1 – 3) × 10 6 c m − 2 were grown by our originally developed quartz-free hydride vapor phase epitaxy method, which enabled the background Si, O, and C concentrations to be suppressed to below the mid-1014 cm−3 range. We prepared three samples with different C concentrations ([C]) by intentional C doping. The C incorporation induced severe mobility collapse at temperatures greater than 60 K, where the measured mobility decreased and deviated from the theoretical value as [C] increased. The mobility collapse was eliminated for the purest GaN crystal with [C] ∼ 1.4 × 10 14 cm − 3 , exhibiting a record high room-temperature mobility of 1480 cm2/(V·s), as well as a record high maximum mobility of 14 300 cm2/(V·s) at 62 K. The latter was almost double the previous record. We found that the overall mobility behavior can be well reproduced by adding an empirical [C]-dependent mobility component expressed as μ UNK = K / T n UNK with 1 ≤ n UNK ≤ 2 and K ∝ C − 1 to the conventional mobility theory (phonon and impurity scattering). Although the mechanism of the component remains uncertain, our findings provide insight into the unsolved issue of mobility collapse. [ABSTRACT FROM AUTHOR]

We demonstrate a dislocation density-based crystal plasticity (CP) model approach for simulating mesoscale deformation and damage. The existing CP framework is extended to be compatible with the oxygen-free phosphorous copper microstructure that is the focus of this study. The key aim is to introduce relevant plastic deformation mechanisms and to develop a failure model capable of depicting creep damage in the material. The effect of local variations in material is evaluated, and the model response is compared with experiments and characterisation. The basis of this work is CP material modelling, including grain orientation and size, obtained using electron backscatter diffraction and experimental test data of real relaxation test specimens. This will yield a realistic description of texture and grain shape and, ultimately, accurate stress–strain response at the microstructural level for further evaluation of performance with respect to material creep(−fatigue) damage. [ABSTRACT FROM AUTHOR]

We consider periodic piecewise affine functions, defined on the real line, with two given slopes and prescribed length scale of the regions where the slope is negative. We prove that, in such a class, the minimizers of s-fractional Gagliardo seminorm densities, with 0

For the first time, a detailed comprehensive study is conducted of the dry etching of dislocation and dislocation-free samples of germanium on planes {111}, {110}, and {100}. Etching is performed by exposure to pulses of nanosecond ultraviolet (UV) laser radiation of the subthreshold intensity (wavelength, 355 nm; duration, ~10 ns; energy density, ~0.5–1.3 J/cm2; pulse repetition rate, 100 Hz; and divergence, 1–2 mrad). Before and after the laser heat treatment of the surface, the samples are examined using a Zygo optical profilometer and a scanning electron microscope. Features of the nature of the damage to the surfaces corresponding to different crystallographic planes of single crystals of industrial dislocation germanium are revealed. They are compared with the data on the subthreshold damage of typical dislocation-free crystals. It is shown that in dislocation samples of germanium on the {111} plane, it is possible to create a regime of exposure to radiation, leading to the formation of etch pits, which is outwardly identical to the dislocation pits detected during selective chemical etching. Their concentration corresponds in order of magnitude to the density of dislocations. On the {100} plane of dislocation samples, etching results are also found, which clearly have a crystallographic nature. At the energy density of the acting radiation ≥0.4 J/cm2 on the surfaces of dislocation (plane {100}) and dislocation-free germanium (planes {111}, {100}, {110}), only individual spots of ~50 µm and individual microcraters of ~0.1–1 µm having crystallographic features are recorded. The possibility of the environmentally friendly detection of dislocations in germanium without the use of chemical reagents is shown. [ABSTRACT FROM AUTHOR]

An Mw 6.8 earthquake occurred in Luding County, Ganzi Tibetan Autonomous Prefecture, Sichuan Province, on 5 September 2022. This seismic event triggered numerous coseismic geohazards in the seismic zone. In this study, the ascending- and descending-track synthetic aperture radar (SAR) images observed by the Sentinel-1A satellite are utilized to extract the coseismic surface deformation of the Luding earthquake. Subsequently, a faulting model is estimated based on the elastic dislocation theory, under the constraint of the InSAR observation. Additionally, the POT technique was employed to detect coseismic geohazards. High-spatial-resolution optical remote sensing images served to validate the reliability of the detection results. The coseismic interferometric synthetic aperture radar (InSAR) deformation field indicated a maximum deformation of ~190 mm and ~140 mm along the ascending and descending tracks, respectively. The estimated best-fitting faulting model suggests that the optimal seismogenic fault strike and dip angles are 169.3° and 70°, respectively. The fault slip predominantly exhibits left-lateral strike-slip characteristics and is concentrated at depths of 3–12 km. The estimated maximum fault slip was 2.67 m, occurring at a depth of 7 km. The pixel offset tracking (POT) result derived from the pre- and post-earthquake SAR images found a total of 245 medium- to large-scale coseismic geohazards, with a verification rate from optical images exceeding 64%. The distribution of these geohazards is notably dense within the significant fault rupture segment. Geohazards on the fault hanging wall are densely packed, whereas landslides along the Dadu River's fault footwall are also notably frequent. [ABSTRACT FROM AUTHOR]

Magnesium alloys with high damping, high specific strength and low density have attracted great attention in recent years. However, the application of magnesium alloys is limited by the balance between their mechanical and damping properties. The strength and plasticity of magnesium alloys with high damping performance often cannot meet the industrial requirements. Understanding the damping mechanism of magnesium alloys is significant for developing new materials with high damping and mechanical properties. In this paper, the damping mechanisms and internal factors of the damping properties of magnesium alloys are comprehensively reviewed. Some damping mechanisms have been studied by many scholars, and it has been found that they can be used to explain damping performance. Among existing damping mechanisms, the G-L dislocation theory, twin damping mechanism and interface damping mechanism are considered common. In addition, some specific long-period stacking ordered (LPSO) phases' crystal structures are conducive to dislocation movement, which is good for improving damping performance. Usually, the damping properties of magnesium alloys are affected by some internal factors directly, such as dislocation density, solute atoms, grain texture and boundaries, etc. These internal factors affect damping performance by influencing the dissipation of energy within the crystal. Scholars are working to find novel damping mechanisms and suitable solute atoms that can improve damping performance. It is important to understand the main damping mechanisms and the internal factors for guiding the development of novel high-damping magnesium alloys. [ABSTRACT FROM AUTHOR]

Hot rolling is an emerging post-processing method for improving mechanical properties of cold sprayed materials. However, the effects of hot rolling on cold sprayed materials are not well clarified. Accordingly, hot rolling assisted with heat treatment was conducted to investigate the effects of hot rolling on plastic deformation of cold sprayed copper bulks. The porosity, crystal grains and dislocation density of copper bulks were characterized through scanning electron microscope, electron back-scatter diffraction and transmission electron microscope. The evolution of pores during hot rolling was simulated using finite element analysis. The microhardness, tensile strength and breaking elongation of the bulks were measured to further explore the effects of hot rolling. The results show that the apparent porosity of the copper bulks sharply decreased due to the dynamic generation and healing processes of the pores in hot rolling. The tensile strength of the copper bulks increased significantly due to the evolution of bonding mechanisms and grain sizes of the copper bulks in hot rolling. [ABSTRACT FROM AUTHOR]

In order to meet the demand for low-absorption sapphire crystal materials in important national defense projects in China, a self-produced crystal growth apparatus is developed in this study and the successful growth of low-absorption sapphire crystal can be achieved. The as-obtained crystal exhibits excellent transparency in the ultraviolet, visible, and near to midinfrared wavelength ranges. The transmittance is above 83% as the wavelength in the range of 250 nm to 400 nm, while the transmittance is above 85% as the wavelength in the range of 400 nm to 4 200 nm. On the basis of the characterization tests conducted on different regions of the crystal, the average dislocation density of crystal can be determined as 253. 19 cm-2. The rocking curve shows symmetrical and sharp peaks with a full width at half maximum of 14". In addition, it is worth noting that the light absorption coefficient of crystal is (23.3 -30.4) x 10-6 cm-1 at the wavelength of 1 064 nm, indicating that the impurity elements inside the crystal can be effectively controlled. Accordingly, the outstanding optical properties crystal can be applied in high-energy laser systems, space camera lenses and other relevant fields. [ABSTRACT FROM AUTHOR]

We consider a semi-linear integro-differential equation in dimension one associated to the half Laplacian whose solution represents the atom dislocation in a crystal. The equation comprises the evolutive version of the classical Peierls–Nabarro model. We show that for a large number of dislocations, the solution, properly rescaled, converges to the solution of a fully nonlinear integro-differential equation which is a model for the macroscopic crystal plasticity with density of dislocations. This leads to the formal derivation of the 1-D Groma–Balogh equations (Groma–Balogh in Acta Mater 47(13):3647–3654, 1999), a popular model describing the evolution of the density of positive and negative oriented parallel straight dislocation lines. This paper completes the work of Patrizi and Sangsawang (Nonlinear Anal 202:112096, 2021). The main novelty here is that we allow dislocations to have different orientation and so we have to deal with collisions of them. [ABSTRACT FROM AUTHOR]

This paper focused on fracture problem about interfacial transition zone (ITZ) formed after repairing between magnesium phosphate cement (MPC) mortar and old Portland cement concrete (PCC) pavements. Firstly, the mode Ⅱ cracks on the ITZ were hypothesized and the interface fracture model with dislocation theory was proposed. The stress field at the crack tip was represented by Airy stress potential function and Fourier Transform, and the structural characteristics of the kernel solution of Cauchy were retained. Then, combined with the oscillation term, the Dirac function was replaced by the normal distribution function to obtain stable fracture parameters. Besides, the ϵ about 8 ‰ of the crack length in model was analyzed. Secondly, the elastic moduli of ITZs were obtained by nanoindentation experiments. Results showed the elastic modulus of ITZ between MPC mortar and ITZ-1 (the interface in concrete) was lowest. Such weakest position in repair interface was further verified by finite element analysis (FEA). Finally, a twodimensional model was developed to validate the fracture model. Simulation results were found consistent with the theoretical solution of interface fracture model. The developed interface fracture model can provide insights for evaluating the shear behavior of the interface between MPC mortar and concrete. [ABSTRACT FROM AUTHOR]

The present study explores the preparation of Al–10wt.%Zn alloy by the casting process. Nano CuO was prepared by the Co-precipitation method. The effect of adding nanostructure of (1wt.% CuO) to Al–10Zn alloy was studied the corrosion effects as-cast and with different aging temperatures (423, 443, and 463 K) for 2 h in 3.5% NaCl aqueous solution after homogenized for 2 h at 500 K at room temperature. Electrochemical measurements (OCP, Tafel, and EIS) were performed to determine the corrosion rate (C.R.) and corrosion current density (Icorr.) to find out corrosion behavior. In addition, microstructures of Al–10Zn and Al–10Zn–1CuO were observed using a scanning electron microscope, EDX mapping, and the optical microscope to investigate the effect of the nanoparticle's addition before and after aging and the corrosion test. The average crystal size and the dislocation density were calculated from the XRD pattern. The results show that the appropriate addition of CuO nanoparticles can refine the Al–10Zn alloy and shift the Al–10Zn alloy to a more noble direction. [ABSTRACT FROM AUTHOR]

Electro-mechanical interactions between topological defects and domain walls play a key role in the macroscopic response of bulk and thin-film ferroelectrics. The applications of ferroelectrics are derived from their inherent ability to nucleate new domains and to move the domain walls that separate adjacent domains. Here, we report dislocation-mediated domain nucleation in single-crystal BaTiO3, achieved by dislocations generated via high-temperature uniaxial compression on a notched sample. We also present a direct observation of domain-wall pinning of 90° ferroelastic domain walls by dislocations using in situ transmission electron microscopy. Dense and well-aligned "forest" dislocations, featuring {100}⟨100⟩ slip systems oriented in the out-of-plane [001] direction, exclusively nucleate in-plane domain variants. We reveal that the 90° domain walls are strongly pinned by imprinted dislocations due to the presence of their associated stress fields. Our findings may advance our understanding of the control of defects in ferroelectrics and propose a strategy applicable to both emerging nanoelectronic and bulk applications. [ABSTRACT FROM AUTHOR]

This paper is concerned with the image force in cubic piezoelectric quasicrystal semi-infinite space and infinite space containing two dissimilar quasicrystal half-spaces. On the basis of the Stroh formalism, the expressions of the Green's function for generalized displacement and stress under multi-physical loading conditions are obtained exactly. Also, the image force applied to a generalized line dislocation with different boundary conditions is taken into account. The image force for the traction-free and electrically open surface always attracts dislocation to the boundary, while that for clamped and electrically closed surface shows the opposite tendency. Illustrative examples, such as generalized line force and line charge, are given to present the mechanical behaviors of quasicrystals under different loading conditions and investigate the influences of material parameters and dislocation scheme on image force. The results show that generalized line force has little effect on atomic configurations, and image force F is the strongest when phonon and phason dislocations interact together. [ABSTRACT FROM AUTHOR]

This paper focused on fracture problem about interfacial transition zone (ITZ) formed after repairing between magnesium phosphate cement (MPC) mortar and old Portland cement concrete (PCC) pavements. Firstly, the mode Ⅱ cracks on the ITZ were hypothesized and the interface fracture model with dislocation theory was proposed. The stress field at the crack tip was represented by Airy stress potential function and Fourier Transform, and the structural characteristics of the kernel solution of Cauchy were retained. Then, combined with the oscillation term, the Dirac function was replaced by the normal distribution function to obtain stable fracture parameters. Besides, the ϵ about 8 ‰ of the crack length in model was analyzed. Secondly, the elastic moduli of ITZs were obtained by nanoindentation experiments. Results showed the elastic modulus of ITZ between MPC mortar and ITZ-1 (the interface in concrete) was lowest. Such weakest position in repair interface was further verified by finite element analysis (FEA). Finally, a twodimensional model was developed to validate the fracture model. Simulation results were found consistent with the theoretical solution of interface fracture model. The developed interface fracture model can provide insights for evaluating the shear behavior of the interface between MPC mortar and concrete. [ABSTRACT FROM AUTHOR]

One strategy for decreasing the density of threading dislocations penetrating the surface of a heteroepitaxial semiconductor film is that in which the greater mechanical stiffness of a dislocation blocking layer acts to reduce the Peach–Koehler image forces acting on the leading segment of the half loop generated by dislocation multiplication sources at the heteroepitaxial interface situated below the blocking layer. Reducing the Peach–Koehler force, drawing the half loop to the film surface, helps prevent the two threading arms of the half loop from becoming threading dislocations once the half loop penetrates the film surface. The calculation of the Peach–Koehler force employs an analytical continuation formalism using anisotropic elasticity theory for treating dislocation image forces generated by three heteroepitaxial interfaces corresponding to the top and bottom interfaces of the blocking layer and the film surface. The system used in this calculation is that of a Ge film grown on a (001) Si substrate, using a SiGe blocking layer just below the critical thickness for dislocation generation. It is found that the dislocation blocking is favored by thinner blocking layers of greater mechanical stiffness, rather than thicker blocking layers of moderate mechanical stiffness. Specifically, for the blocking layers of composition Si0.2Ge0.8, Si0.3Ge0.7, and Si0.4Ge0.6, of thickness 50, 18, and 10 nm, respectively, it is the thinnest (and mechanically stiffest) layer (Si0.4Ge0.6, 10 nm) that brings about the greatest reduction in the Peach–Koehler force, drawing the leading segment of the half loop to the surface of the film. [ABSTRACT FROM AUTHOR]

The motion of line defects (dislocations) has been studied for more than 60 years, but the maximum speed at which they can move is unresolved. Recent models and atomistic simulations predict the existence of a limiting velocity of dislocation motion between the transonic and subsonic ranges at which the self-energy of dislocation diverges, though they do not deny the possibility of the transonic dislocations. We used femtosecond x-ray radiography to track ultrafast dislocation motion in shock-compressed single-crystal diamond. By visualizing stacking faults extending faster than the slowest sound wave speed of diamond, we show the evidence of partial dislocations at their leading edge moving transonically. Understanding the upper limit of dislocation mobility in crystals is essential to accurately model, predict, and control the mechanical properties of materials under extreme conditions. [ABSTRACT FROM AUTHOR]

The East Kunlun fault zone (EKFZ), located northeast of the Qinghai–Tibet Plateau, has experienced several strong earthquakes of magnitude seven or above since 1900. It is one of the most active fault systems and is characterized by left-lateral strike-slip. However, the Xidatan–Dongdatan segment (XDS) of the East Kunlun fault zone (EKFZ) has had no earthquakes for many years, and the Kunlun Mountains MS 8.1 earthquake has a stress loading effect on this segment, so it is widely regarded as a high-risk earthquake gap. To this end, we collected the Sentinel-1 data of the XDS of the EKFZ from July 2014 to July 2019 and obtained the high-precision interseismic deformation field by the Interferometric Synthetic Aperture Radar (InSAR) technique to obtain the slip rate and locking depth of the XDS of the EKFZ, and the seismic potential of the segment was analyzed. The results are as follows: (1) The LOS deformation field of the XDS of the EKFZ was obtained using Sentinel-1 data of ascending and descending orbits, which indicated that the XDS of the EKFZ is dominated by horizontal motion. Combined with the interference results, it is shown that the strike-slip rate dominates the deformation information of the XDS of the EKFZ. The deep strike-slip rate of the fault is about 6 mm/yr, the deep dip-slip rate is about 2 mm/yr, and the slip-deficit rate on the fault surface is about 6 mm/yr; (2) Combined with the spiral dislocation theory model, the slip rate of the XDS to Xiugou Basin of the EKFZ has a gradually increasing trend, with an average slip rate of 9.6 ± 2.3 mm/yr and a locking depth of 29 ± 5 m; (3) The stress accumulation is about 483 ± 92 years in the XDS of the EKFZ, indicating that the cumulative elastic strain energy of the XDS can produce an MW 7.29 ± 0.1 earthquake in the future. [ABSTRACT FROM AUTHOR]

Background: This research was conducted in response to concerns reported by social work practitioners to a Canadian College of Social Work which indicated that their practice was constrained by ideological and system limitations in publicly funded mental health and addiction systems. Method: The dislocation theory of addiction which posits globalization and neoliberalism is linked to addiction rates worldwide, serves as an analytical frame to examine findings from fifty interviews, three focus groups and an online survey with one hundred and fifteen respondents. Results: Themes specific to social work practice in addiction services referred to neoliberalism, stigma, biomedicalization, trauma and addiction, elimination of women services, shrinking services and privatization. Conclusion: Social workers expressed a dissonance between their training rooted in relational approaches and biopsychosocial models of practice and system expectations. Our findings indicate concern about the erosion of core social work values within addiction services, the reduction of state funded programming and need for further research. [ABSTRACT FROM AUTHOR]

An atomic-scale approach was employed to simulate the formation of precipitates with different lattice misfits in the early stages of the aging of supersaturated aluminum alloys. The simulation results revealed that the increase in lattice misfits could significantly promote the nucleation rate of precipitates, which results in a larger number and smaller size of the precipitates. The morphologies of the precipitates also vary with the degree of a lattice misfit. Moreover, the higher the lattice misfit, the earlier the nucleation of the second phase occurs, which can substantially inhibit the movement of dislocations. The research on the lattice misfit of precipitation can provide theoretical guidance for the design of high-strength aluminum alloys. [ABSTRACT FROM AUTHOR]

The Gravity Recovery and Climate Experiment (GRACE) mission and its successor GRACE Follow‐On (GRACE‐FO) mission provide humans with a unique perspective on mass distribution through accurate temporal gravity field models. However, these models suffer from unavoidable stripe errors in the spatial domain. A new approach based on image processing has been developed for filtering GRACE and GRACE‐FO spherical harmonic solutions. In this approach, the gravity fields are treated as noise‐contaminated images, and the stripe errors are expected to be suppressed by convolving the input with an appropriate kernel. To verify the effectiveness of the proposed approach, a closed‐loop simulation environment over the nominal mission lifetime of 5 years is designed. Image processing indicators and geophysical information evaluation results demonstrate the superior performance of the new approach in suppressing stripe errors. In the context of real GRACE data processing, our new approach still yields better results as follows: (a) The comprehensive ability of de‐striping and retaining details has slight advantages over some commonly used filters, as demonstrated through spatial distributions, amplitude spectra, and coefficient spectra. (b) The equivalent water height time series at the basin scale is comparable to the results derived from other filters or Level‐3 products. (c) The estimated signal amplitude of the Mw9.1 2004 Sumatra earthquake co‐seismic gravity change is 52.7% larger than that derived from the Gaussian 300 km filter, which is much closer to the theoretical value derived from the dislocation theory. Plain Language Summary: Mass migration inside the Earth and at its surface generates global gravitational variations. The GRACE mission pioneers a novel path of monitoring global gravitational variations from satellites. Since the raw GRACE data is highly noisy, it must be filtered before application. This study reports a new filtering approach that utilizes the method of image processing. Different from the traditional method, the new approach adopts adjustments not based on spherical harmonic coefficients. The quantitative assessments via simulation studies demonstrate the good performance of our proposed method from both the perspective of image processing and geophysical signal analysis. To illustrate the practical effect of our method, we then use it to filter the real GRACE data. The extensive comparisons also support the effectiveness of our method. In practical research, such as detecting earthquake gravity signals, we obtain more realistic results than those derived from traditional approaches. All results indicate that our method performs well in noise suppression and signal preservation. Overall, the proposed method can be considered as an important option in GRACE data filtering. Key Points: A new Gravity Recovery and Climate Experiment (GRACE) filtering approach based on the spectral features of longitudinal stripe errors is designedThe proposed approach demonstrates good performance in terms of signal preservation and suppression of stripe errorsEvaluations based on image processing analysis and geophysical information indicate the effectiveness of our method [ABSTRACT FROM AUTHOR]

Due to the inevitable formation of the second phase of Te in the growth process of Cadmium zinc telluride (CdZnTe/CZT) crystal, the Te related defects are usually treated by Cd atmosphere annealing to improve the crystal quality. In this paper, the influence of different powder burying crystals on the annealing effect in Cd atmosphere is studied by analyzing the change of crystal surface components, removal effect of Te inclusion, electric field distribution and carrier transport characteristics. The results show that burying the crystal with powder helps to maintain the crystal surface composition in annealing, but the Te inclusion can be eliminated only by controlling the amount of powder. Moreover, it is found that the uniformly distributed Te inclusions tend to migrate to the surface during the annealing process, while the Te inclusions at dislocation or crystal boundary are difficult to eliminate. It is speculated that the internal Te loading is more inclined to the reaction of diffused Cd atom, which makes the Te inclusions decrease continuously. After annealing with proper amount of powder, due to the elimination of Te inclusion defects, the electric field distribution inside the crystal is more uniform and the carrier lifetime product is improved. [ABSTRACT FROM AUTHOR]

The present study explores the preparation of Al–10wt.%Zn alloy by the casting process. Nano CuO was prepared by the Co-precipitation method. The effect of adding nanostructure of (1wt.% CuO) to Al–10Zn alloy was studied the corrosion effects as-cast and with different aging temperatures (423, 443, and 463 K) for 2 h in 3.5% NaCl aqueous solution after homogenized for 2 h at 500 K at room temperature. Electrochemical measurements (OCP, Tafel, and EIS) were performed to determine the corrosion rate (C.R.) and corrosion current density (Icorr.) to find out corrosion behavior. In addition, microstructures of Al–10Zn and Al–10Zn–1CuO were observed using a scanning electron microscope, EDX mapping, and the optical microscope to investigate the effect of the nanoparticle's addition before and after aging and the corrosion test. The average crystal size and the dislocation density were calculated from the XRD pattern. The results show that the appropriate addition of CuO nanoparticles can refine the Al–10Zn alloy and shift the Al–10Zn alloy to a more noble direction. [ABSTRACT FROM AUTHOR]

The problem of passage of a plane harmonic wave through the interface of elastic-plastic bodies with dislocations is considered. The continuum model obtained in the framework of the Lagrangian formalism and gauge dislocation theory is used to describe the studied bodies. According to this model, the shear wave in an elastic-plastic body with dislocations propagates in the form of coupled waves of transverse displacements and shear components of the plastic distortion tensor. Using the asymptotic method of slowly varying amplitude and the dispersion relations of the wave under consideration, analytical expressions are found for the reflection and refraction coefficients under various boundary conditions in the simplest case of the normal incidence of the primary wave. The dependences of the Fresnel coefficients on the frequency of the wave incident on the interface of the elastic-plastic bodies under condition of their ideal contact, sliding, viscous friction, and imperfect contact are calculated. The influence of the elastic parameters of the model and the constants of the dislocations continuum on the processes of shear waves passing through the interface of the elastic-plastic bodies under the considered boundary conditions is analyzed. [ABSTRACT FROM AUTHOR]

Creating alloys with a gradient microstructure in grain size has been shown to be a potential method to resolve the trade-off dilemma between strength and ductility. However, different textures developed with various processing methods cannot be fully eliminated, which can significantly affect the mechanical behavior of alloys. In this study, we use a multiscale framework based on dislocation theory to investigate how the combination of rolling texture and gradient in grain size affects the plastic deformation of nano-gradient aluminum during a tensile test. We found that specific rolling textures, such as {110} texture, can significantly enhance the strength and ductility of nano-gradient aluminum. This improvement is the result of the grain being reoriented and the redistribution of stress and strain, which are caused by the combined influence of texture and variation in grain size. These results provide new insights into developing high-performance aluminum by mediating texture and grain size gradient. [ABSTRACT FROM AUTHOR]

A mechanically coupled diffusion model combined with finite element formulation is developed to study the influence of dislocations on ion diffusion in lithium-ion batteries. The dislocation is modeled by the regularized eigenstrain based on a non-singular continuum dislocation theory. The model is validated with the analytical solution of the stress field of edge dislocations and the solution for the stress-dependent equilibrium concentration around the dislocation. Simulation results on LiMn 2 O 4 demonstrate strong ion enrichment and depletion on the tensile and compressive sides of an edge dislocation, respectively. A stronger influence of the edge dislocation on diffusion is found at a lower state-of-charge, which verifies the experimental observation reported in the literature. The diffusion-induced stress compensates partially the stress field of the edge dislocation and is ascertained to have a state-of-charge dependency. The existence of dislocation does not introduce obvious mobility anisotropy in the bulk material but it results in local mobility heterogeneity around the dislocation. A three-dimensional simulation of the diffusion along the edge dislocation line reveals that the pipe diffusion can be initiated or accelerated on the tensile side of the edge dislocation. [ABSTRACT FROM AUTHOR]

The core structures of dislocations are crucial for understanding the plastic deformation mechanisms and the functional properties of materials. Here, we use the scanning transmission electron microscopy imaging techniques of high-resolution high angle annular dark field and integrated differential phase contrast to investigate the atomic structure of a pair of climb-dissociated 1 2 a [ 01 1 ¯ ] dislocations in a bending-deformed relaxor ferroelectric Pb(In1/2Nb1/2)O3–Pb(Mg1/3Nb1/3)O3–PbTiO3 single crystal. Cations at one dislocation core are found to arrange in the same way as the climb-dissociated 1 2 a [ 01 1 ¯ ] dislocation core in SrTiO3, while the other one is different. Oxygen depletion was observed at both dislocation cores. Geometric phase analysis of the lattice rotation shows opposite signs at both sides of the dislocations, demonstrating the strain gradient, which is known to give rise to flexoelectric polarization. Using the peak finding method, the polarization (a combination of ferroelectric and flexoelectric) around dislocations was mapped at the unit-cell scale. The polarization direction obtained is consistent with that predicted based on the flexoelectric effect in a perovskite oxide with [011] geometry. Head-to-head positively charged and tail-to-tail negatively charged domain walls were revealed based on the polarization map, suggesting a new way to stabilize charged domain walls via dislocations. A distinct dislocation core configuration has been observed, and a unit-cell scale polarization map helps understand the flexoelectric effects (coupling between strain gradient and polarization) around dislocations in a relaxor ferroelectric. [ABSTRACT FROM AUTHOR]

As an improvement of the conventional misfit dislocation theory, a theoretical self-consistent method is presented for a study of the heterojunction. Although the interaction between two adhesive crystals is still effectively described by the γ -energy function, however, the period appearing in the γ -energy function is no longer predetermined as is usually done but treated as a parameter needs to be determined in a self-consistent way. Because the period is actually the Burgers vector of the misfit dislocation, the self-consistent method is significant for the dislocation-based heterojunction theory. As an illustration, the theory is applied to the heterojunction of two-dimensional materials AlN and BN. It is found that for the AlN/BN heterojunction, the period determined from the minimum-energy principle is very close to the value given previously. [ABSTRACT FROM AUTHOR]

A 4H-SiC single crystal is a substrate material for high-frequency and high-voltage power devices. Dislocation density is a fundamental criterion for evaluating the quality of 4H-SiC single crystals. 4H-SiC single crystals grown by the physical vapor transport (PVT) method generally have high dislocation density. To investigate the effect of nitrogen doping on dislocation proliferation in SiC crystals, the thermal field of the ingot during PVT growth was calculated by COMSOL Multiphysics, and thermal stress was calculated by thermal elastic theory. Finally, the dislocation density of the crystal was calculated based on the Alexander–Haasen model for inhomogeneous nitrogen doping. By comparing the calculation and experimental results, we proposed a possible value of the effective stress to evaluate the effect of a nitrogen dopant on dislocation density, which helps calculate the dislocation density in the n-type SiC. [ABSTRACT FROM AUTHOR]

The fundamental properties of dislocations in diamond-structured Si and sphalerite-structured GaAs, InP and CdTe are investigated based on lattice theory of dislocation, hoping to provide some theoretical references in improving the properties of related materials. The influences of the surface effect(SE) and elastic strain energy on the structure and mechanical property of dislocation are discussed systematically. After considering the SE, the core width of dislocation becomes wider due to the elastic interaction between atoms becomes stronger. Compared to glide partial dislocation, the correction of SE to shuffle dislocation is more obvious. Both the SE and the elastic strain energy affect the energy barrier and Peierls stress of dislocation. The influence of SE on energy barrier and Peierls stress mainly results from the misfit energy and elastic strain energy become lower when the core of dislocation becomes wider. While the influence of elastic strain energy on energy barrier and Peierls stress mainly results from the cancellation between misfit energy and elastic strain energy for they possess comparable amplitudes but opposite phases. In addition, it is deduced that for the studied crystals, the shuffle dislocations control the deformation at medium and low temperatures, while glide partial dislocations are responsible for high temperature plasticity. [ABSTRACT FROM AUTHOR]

We derive strain-gradient plasticity from a nonlocal phase-field model of dislocations in a plane. After scaling, from the nonlocal elastic interaction we derive a continuous energy with linear growth depending on a measure which characterizes the macroscopic dislocation density as well as a nonlocal effective energy representing the far-field interaction between dislocations. Relaxation and formation of microstructures at intermediate scales are automatically incorporated in the limiting procedure based on Γ-convergence. [ABSTRACT FROM AUTHOR]

Combining the advantages of high thermal conductivity, large emission bandwidth and appropriate emission crosssection, the fluorite-type laser crystal Nd, Y ∶ SrF2 (NYSF) has important application in high-power laser techniques. Dislocation in laser crystals is an important category of microscopic defects which implies the integrity of crystalline lattice structure, and influences the mechanical and optical performances of crystals. The NYSF crystals were grown by vertical Bridgman method and the optimized experimental parameters for chemical etching of dislocation defects were obtained by comparing the influence of various etching conditions on the morphology of etch pits in in NYSF crystals. The optimized etching condition are: concentration of 4 mol/L hydrochloric acid solution as a corrosive solution and corrosion temperature of 60 ℃ and corrosion time of 9 ~ 12 min. The evolution of dislocation etch pit morphology was studied and the relationship between the lattice structure and the morphology of etch pits was analyzed. The distribution of dislocation defects in NYSF was characterized by chemical etching method. The axial distribution first decreases and then increases from the shouldering to the tail, and the radial distribution gradually increases from the center to the edge. The influence of crystal growth processes on the formation of defects was discussed and the possible reason why dislocation density increases with increasing crucible drop rate was proposed. [ABSTRACT FROM AUTHOR]

We discuss the theoretical solution to the differential equations governing accelerating edge dislocations in anisotropic crystals. This is an important prerequisite to understanding high-speed dislocation motion, including an open question about the existence of transonic dislocation speeds, and subsequently high-rate plastic deformation in metals and other crystals. [ABSTRACT FROM AUTHOR]