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We present an efficient approach to evaluate the size dependency of elastic and plastic properties of metallic polycrystalline materials. Specifically, we consider different volume fractions of ferrite and martensite phases for the construction of three macroscopic domains. Statistical Volume Elements (SVEs) of different sizes are extracted from these domains using the moving window method. Linear and Crystal Plasticity (CP) simulations provide elastic and plastic properties of the SVEs such as the bulk and shear moduli, yield strength, and hardening modulus. We use a variation-based criterion to determine the Representative Volume Element (RVE) size of these properties. This RVE size corresponds to a size beyond which the given property can be idealized as homogeneous. We also use anisotropy indices and an additional RVE size criterion to determine the size limits beyond which these properties can be idealized as isotropic. Numerical results show that the plastic properties often reach their homogeneity and isotropy limits at larger sizes compared to elastic properties. This effect is more pronounced for the hardening modulus compared to the yield strength. [ABSTRACT FROM AUTHOR]

Nanoscale defects can induce the effective modulation of carrier concentration, mobility, and phonon scattering to secure high thermoelectric performance in semiconductors. However, it is still limited to effectively controlling nanoscale defects in thermoelectric materials. Here, argon plasma bombardment is employed to introduce a large number of point defects and dislocations in microcrystalline SnSe powders, synthesized by a solvothermal method. After sintering these powders into polycrystalline bulk materials, bulk SnSe shows the ZT increasing by up to 66.7% (from 0.36 to 0.6 at 773 K). Through detailed micro/nanostructure characterizations and first‐principles calculations, the underlying mechanism is elucidated for the evaluation of thermoelectric performance. This work provides a deep understanding of the mechanism of nanoscale defects in modulating thermoelectric performance and presents experimental evidence and experience for the design and synthesis of efficient thermoelectric materials, making significant contributions to future green energy technologies. [ABSTRACT FROM AUTHOR]

The quantitative relationship between material microstructures, such as grain distributions, and the nonlinear strain-hardening behaviors of polycrystalline metals has not yet been completely understood. This study finds that the grain correlation dimension of polycrystals D is universally equal to the reciprocal of the strain-hardening exponent by experimental research and fractal geometry analysis. From a geometric perspective, the correlation dimension of grains is consistent with that of the equivalent plastic strain field, which represents the correlation dimension of the material manifold. According to the definition of the Hausdorff measure and Ludwik constitutive model, the strain-hardening exponent represents the exponent derived from the Dth root of the measure relationship. This universal law indicates that the strain-hardening behaviors are fractal geometrized and that the strain-hardening exponent represents a geometrical parameter reflecting the multifractal characteristics of grain structures. This conclusion can enhance the comprehension of the relationship between microstructure and mechanical properties of materials and highlights the importance of designing materials with non-uniform grain distributions to achieve desired hardening properties. [ABSTRACT FROM AUTHOR]

In this paper, type-Ib diamond single crystals, using two different sizes of synthesis cavities of ϕ15 mm and ϕ30 mm, were synthesized under 5. 7 GPa, 1 560 ~ 1 600 K, and the temperature field distributions of the two sizes of synthesis cavities were studied using finite element method (FEM). Firstly, the temperature field distributions of two different sizes of synthesis cavities were simulated using finite element method. The average radial temperature gradient and average axial temperature gradient of the ϕ15 mm synthesis cavity are 0. 573 and 5. 700 K/mm, respectively. The average radial temperature gradient and average axial temperature gradient of the ϕ30 mm cavity are 0. 093 and 2. 280 K/mm, respectively. The simulation results reveal that the uniformity of the temperature field in the ϕ30 mm synthesis cavity is significantly better than that in the ϕ15 mm synthesis cavity. Secondly, the reproducible growth of high-quality type-Ib diamond large single crystals was achieved using both synthesis cavities mentioned above. The ϕ15 mm synthetic cavity is difficult to achieve the growth of high-quality type-Ib diamond single crystals weighing more than 1. 2 ct (1 ct =0. 2 g), while the ϕ30 mm synthetic cavity is more suitable for the growth of large-size high-quality type-Ib diamond single crystals. Furthermore, the scanning electron microscopy (SEM) test results show that the surface flatness of high-quality type-Ib diamond single crystals grown using two different sizes of synthesis cavities in this study is good, and the expansion of the synthesis cavity has no significant effect on the crystal quality of Ib diamond single crystal surface. Finally, Raman spectrum test results show that the crystal quality of polycrystalline diamond deteriorates, and other diamond single crystal samples synthesized by two kinds of synthesis cavity in this study have better crystal quality. This research has certain academic reference value for the design of large size synthesis cavity of gem grade diamond single crystal, the growth of large size diamond single crystal, and the perfection of polycrystalline diamond single crystal synthesis technology. [ABSTRACT FROM AUTHOR]

Biominerals formed by animals are most frequently calcium carbonate or phosphate polycrystalline materials with complex hierarchical structures. This article will focus on the 10-nm–10-µm scale, termed “mesoscale,” at which the “mesostructure” differs greatly across biominerals, is relevant to their mechanical properties, and reveals formation mechanisms in sea urchin teeth, mollusk shell prisms and nacre, human enamel, and coral skeletons. This article will conclude by focusing on important unanswered questions to inspire future research. Graphical abstract: [Figure not available: see fulltext.].

This study provides a methodology for exploring the microstructural and mechanical properties of the Haynes®282® alloy produced via the Powder Bed Fusion-Electron Beam (PBF-EB) process. Employing 2D Electron Backscatter Diffraction (EBSD) data, we have successfully generated 3D representations of columnar microstructures using the Representative Volume Element (RVE) method. This methodology allowed for the validation of elastic properties through Crystal Elasticity Finite Element (CEFE) computational homogenization, revealing critical insights into the material behavior. This study highlights the importance of accurately representing the grain morphology and crystallographic texture of the material. Our findings demonstrate that created virtual models can predict directional elastic properties with a high level of accuracy, showing a maximum error of only ~5% compared to the experimental results. This precision underscores the potential of our approach for predictive modeling in Additive Manufacturing (AM), specifically for materials with complex, non-homogeneous microstructures. It can be concluded that the results uncover the intricate link between microstructural features and mechanical properties, underscoring both the challenges encountered and the critical need for the accurate representation of grain data, as well as the significance of achieving a balance in EBSD area selection, including the presence of anomalies in strongly textured microstructures. [ABSTRACT FROM AUTHOR]

A physics-based model on polarization switching in ferroelectric polycrystalline films is proposed. The calculation results by the model agree well with experimental results regarding dynamic operations of ferroelectric-gate field-effect transistors (FeFETs). In the model, an angle θ for each grain in the ferroelectric polycrystal is defined, where θ is the angle between the spontaneous polarization and the film normal direction. Under a constant electric field for a single-crystal film with θ = 0, phenomena regarding polarization domain nucleation and wall propagation are well described by the Kolmogorov–Avrami–Ishibashi theory. Since the electric fields are time-dependent in FeFET operations and the θ values are distributed in the polycrystalline film, the model in this paper forms an extended Kolmogorov–Avrami–Ishibashi (EKAI) model. Under a low electric field, the nucleation and domain propagation proceed according to thermally activated processes, meaning that switching the time scale of a grain with the angle θ is proportional to an exponential form as e x p (c o n s t. / E z c o s θ) [ E z : the film-normal electric field]. Wide θ distribution makes the time response quite broad even on the logarithmic scale, which relates well with the broad switching time experimentally shown by FeFETs. The EKAI model is physics based and need not assume non-physical distribution functions in it. [ABSTRACT FROM AUTHOR]

Metal halide perovskites (MHPs) have emerged as a highly promising candidate for next-generation light-emitting materials due to their exceptional optoelectronic properties. These properties include superior color purity, high photoluminescence quantum efficiency (PLQY), and the facile tunability of bandgap through compositional and dimensional control. Particularly, polycrystalline perovskites have been introduced as the first perovskite light-emitting diodes (PeLEDs) with superior charge mobility. However, the development of efficient and stable PeLEDs, crucial for commercialization, has proven to be a significant challenge due to the low exciton binding energy (Eb) and inherent defects. Nevertheless, recent achievements have demonstrated polycrystalline PeLEDs with an external quantum efficiency (EQE) surpassing 28% and a half-lifetime (T50) exceeding 30,000 h. In this review, we present the progress of polycrystalline PeLEDs with improved efficiency (PLQY, EQE) and stability by focusing on grain size regulation, defect passivation, and dimensional control. This review offers promising strategies for realizing polycrystalline perovskite material as a light emitter, highlights limitations and provides future perspectives for advancing PeLEDs. [ABSTRACT FROM AUTHOR]

Metal halide perovskites (MHPs) have emerged as a highly promising candidate for next-generation light-emitting materials due to their exceptional optoelectronic properties. These properties include superior color purity, high photoluminescence quantum efficiency (PLQY), and the facile tunability of bandgap through compositional and dimensional control. Particularly, polycrystalline perovskites have been introduced as the first perovskite light-emitting diodes (PeLEDs) with superior charge mobility. However, the development of efficient and stable PeLEDs, crucial for commercialization, has proven to be a significant challenge due to the low exciton binding energy (Eb) and inherent defects. Nevertheless, recent achievements have demonstrated polycrystalline PeLEDs with an external quantum efficiency (EQE) surpassing 28% and a half-lifetime (T50) exceeding 30,000 h. In this review, we present the progress of polycrystalline PeLEDs with improved efficiency (PLQY, EQE) and stability by focusing on grain size regulation, defect passivation, and dimensional control. This review offers promising strategies for realizing polycrystalline perovskite material as a light emitter, highlights limitations and provides future perspectives for advancing PeLEDs.

We present an efficient approach to evaluate the size dependency of elastic and plastic properties of metallic polycrystalline materials. Specifically, we consider different volume fractions of ferrite and martensite phases for the construction of three macroscopic domains. Statistical Volume Elements (SVEs) of different sizes are extracted from these domains using the moving window method. Linear and Crystal Plasticity (CP) simulations provide elastic and plastic properties of the SVEs such as the bulk and shear moduli, yield strength, and hardening modulus. We use a variation-based criterion to determine the Representative Volume Element (RVE) size of these properties. This RVE size corresponds to a size beyond which the given property can be idealized as homogeneous. We also use anisotropy indices and an additional RVE size criterion to determine the size limits beyond which these properties can be idealized as isotropic. Numerical results show that the plastic properties often reach their homogeneity and isotropy limits at larger sizes compared to elastic properties. This effect is more pronounced for the hardening modulus compared to the yield strength.

A new algorithm named PolyCISAMR is introduced to automatically generate high-fidelity conforming finite element (FE) meshes for two-dimensional polycrystalline microstructures. PolyCISAMR extends the capabilities of the Conforming to Interface Structured Adaptive Mesh Refinement (CISAMR) algorithm, which transforms a structured grid overlaid on the domain geometry into a high-quality conforming mesh. The PolyCISAMR approach uses a segregated meshing strategy, where CISAMR is used to discretize each grain independently and the resulting matching meshes are merged to form the final FE model. In addition, this article presents a set of integrated algorithms for processing low-resolution images of a polycrystal, reconstructed using DREAM.3D software (Version 6.5.121), to generate NURBS characterizations for each grain prior to mesh generation. Example problems demonstrate the effectiveness of PolyCISAMR in creating high-quality meshes for various polycrystalline metallic microstructures along with corresponding crystal plasticity finite element (CPFE) simulations. [ABSTRACT FROM AUTHOR]

Wear during dry sliding friction depends on the features of deformation accumulation. The regularities of this process are traced on polycrystalline Hadfield steel with structure certified by Electron Backscatter Diffraction (EBSD). The root mean square values of the vibration acceleration and the friction coefficient change a little during friction. The grain deformation and the volume of the material involved in deformation are increased by friction. The area with deformed grains increases during the first three test cycles. The deformation propagation from the friction surface is slower than in single crystals. The activity of grain deformation is determined by a high value of the Schmid factor for the normal load and the friction force. The values of the shear trace parameters of grains are similar to those of the single crystals. The grain orientation difference and the hardening effect of grain boundaries delay the deformation accumulation and destruction, increasing the wear resistance of the polycrystalline steel compared to the single crystals. [ABSTRACT FROM AUTHOR]

The article is devoted to the study of the mechanism of nanopore formation in the junctions of polycrystal grains under the plastic deformation of a polycrystal due to the conservative sliding of lattice dislocations. A mechanism for the formation of a stress concentrator at the junction of the polycrystal grain boundaries is proposed. The possibility of relaxation of the stress state due to the formation of a junction nanopore is considered in the paper. [ABSTRACT FROM AUTHOR]

The quantitative relationship between material microstructures, such as grain distributions, and the nonlinear strain-hardening behaviors of polycrystalline metals has not yet been completely understood. This study finds that the grain correlation dimension of polycrystals D is universally equal to the reciprocal of the strain-hardening exponent by experimental research and fractal geometry analysis. From a geometric perspective, the correlation dimension of grains is consistent with that of the equivalent plastic strain field, which represents the correlation dimension of the material manifold. According to the definition of the Hausdorff measure and Ludwik constitutive model, the strain-hardening exponent represents the exponent derived from the Dth root of the measure relationship. This universal law indicates that the strain-hardening behaviors are fractal geometrized and that the strain-hardening exponent represents a geometrical parameter reflecting the multifractal characteristics of grain structures. This conclusion can enhance the comprehension of the relationship between microstructure and mechanical properties of materials and highlights the importance of designing materials with non-uniform grain distributions to achieve desired hardening properties.

The article presents data on the study of the effect of substitutions of M-cations in the system of Na3Fe2(1-x)Sc2x(PO4)3 solid solutions (in the concentration range 0 ≤ x ≤ 0.06) on the crystal structure, ionic conductivity, and also on the temperature of phase transitions Tα→β , Tβ→γ . It is shown that samples of Na3Fe2(1-x)Sc2x(PO4)3 (0 ≤ x ≤ 0.06) solid solutions are monoclinically distorted, and the structure parameters increase linearly with increasing dopant concentration. Moreover, in the studied samples of solid solutions, an increase in the conductivity of the α -phase and a decrease in the β - and γ -phases are observed, as well as a decrease in the temperatures Tα→β and Tβ→γ . It is concluded that these changes are associated with both local deformations of the anionic part of the crystalline structure{[Fe2(1-x)Sc2x(PO4)]3−}3∞ , and violation of the regularity of the crystal structure.

The mechanical behavior of a magnesium alloy E-form under bending was investigated using the elasto-visco-plastic polycrystal model (ΔEVPSC) and its finite element (FE) implementation (ΔEVPSC-FE) developed in Jeong et al. and Jeong and Tomé. The crystallographic orientation distribution (COD) obtained from X-ray diffraction was used to represent the initial texture, and the Voce hardening parameters were calibrated by fitting the uniaxial tension and the compression flow stress curves. A quasi-static FE analysis of a miniaturized V-bending operation was conducted using the ΔEVPSC-FE model. The bending induced an inhomogeneous stress response along the through-thickness and the lateral directions, which was well captured by the model. Moreover, the predictive capability of the model was validated by comparing with various experimental results such as (1) force vs. displacement curves; (2) the through-thickness variations in the twin volume fraction; and (3) the changes in crystallographic texture as a function of displacement. Additional bending simulation was performed using an isotropic texture, the result of which suggests that the potential improvement in bendability of the magnesium alloy is attainable by weakening the initial texture. Moreover, the simulation results imply that the crystallographic texture, which may affect the twin activation across the thickness direction, plays a significant role in the shifting direction of the neutral layer.

This study provides a methodology for exploring the microstructural and mechanical properties of the Haynes®282® alloy produced via the Powder Bed Fusion-Electron Beam (PBF-EB) process. Employing 2D Electron Backscatter Diffraction (EBSD) data, we have successfully generated 3D representations of columnar microstructures using the Representative Volume Element (RVE) method. This methodology allowed for the validation of elastic properties through Crystal Elasticity Finite Element (CEFE) computational homogenization, revealing critical insights into the material behavior. This study highlights the importance of accurately representing the grain morphology and crystallographic texture of the material. Our findings demonstrate that created virtual models can predict directional elastic properties with a high level of accuracy, showing a maximum error of only ~5% compared to the experimental results. This precision underscores the potential of our approach for predictive modeling in Additive Manufacturing (AM), specifically for materials with complex, non-homogeneous microstructures. It can be concluded that the results uncover the intricate link between microstructural features and mechanical properties, underscoring both the challenges encountered and the critical need for the accurate representation of grain data, as well as the significance of achieving a balance in EBSD area selection, including the presence of anomalies in strongly textured microstructures.

The deformation-induced surface roughening of an Al-Mg alloy is analyzed using a combination of experiments and modeling. A mesoscale oligocrystal of AA5052-O, obtained by recrystallization annealing and subsequent thickness reduction by machining, that contains approx. 40 grains is subjected to uniaxial tension. The specimen contains one layer of grains through the thickness. A laser confocal microscope is used to measure the surface topography of the deformed specimen. A finite element model with realistic (non-columnar) shapes of the grains based on a pair of Electron Back-Scatter Diffraction (EBSD) scans of a given specimen is constructed using a custom-developed shape interpolation procedure. A Crystal Plasticity Finite Element (CPFE) framework is then applied to the voxel model of the tension test of the oligocrystal. The unknown material parameters are determined inversely using an efficient, custom-built optimizer. Predictions of the deformed shape of the specimen, surface topography, evolution of the average roughness with straining and texture evolution are compared to experiments. The model reproduces the averaged features of the problem, while missing some local details. As an additional verification of the CPFE model, the statistics of surface roughening are analyzed by simulating uniaxial tension of an AA5052-O polycrystal and comparing it to experiments. The averaged predictions are found to be in good agreement with the experimentally observed trends. Finally, using the same polycrystalline specimen, texture–morphology relations are discovered, using a symbolic Monte Carlo approach. Simple relations between the Schmid factor and roughness can be inferred purely from the experiments. Novelties of this work include: realistic 3D shapes of the grains; efficient and accurate identification of material parameters instead of manual tuning; a fully analytical Jacobian for the crystal plasticity model with quadratic convergence; novel texture–morphology relations for polycrystal. [ABSTRACT FROM AUTHOR]

Single- and poly-crystalline semiconductors have quite different photonic and electrical properties. Benefiting from the much lower fabrication cost, poly-crystalline semiconductors attract considerable attention in large-scale applications. However, the effect of polycrystal on plasmonic metal/semiconductor heterostructure has long been ignored. Here, we fabricate Au-antennas/single-crystalline-TiO2 (Au/s-TiO2) and Au-antennas/polycrystalline TiO2 (Au/p-TiO2) samples, and compare the hot electron behaviors in them. An extraordinary sublinear photocurrent with light intensity for the Au/p-TiO2 is observed. Due to the abundant grain boundary of p-TiO2, the hot electron current changes from Schottky-barrier-limited to bulk-limited transport. Moreover, there is a larger Schottky barrier at Au and p-TiO2 interface than that on Au and s-TiO2 interface. This makes the hot carriers recombine mainly in the Au particles of Au/p-TiO2 when a negative bias is applied. These results are highly helpful to improve the performance of plasmonic metal/semiconductor heterostructure for large-scale applications, such as photocatalyst and photovoltaic cell, and are also beneficial for the design of plasmonic devices with special properties. [ABSTRACT FROM AUTHOR]

By using the solid-state reaction approach, composite polycrystalline samples of (Bi0.98In0.02)2Te2.7Se0.3/x%Bi2Se3 were created with varying amounts of Bi2Se3, (x = 5%, 10%, 15%, and 20%). The hexagonal crystal structure of the composite was revealed by x-ray diffraction (XRD) with a space group of R 3 ¯ m. The surface of the samples was seen to have secondary particles using a field emission scanning electronic microscope. Every sample displayed the typical semi-conducting behaviour across the entire temperature range. In the complex (Bi0.98In0.02)2Te2.7Se0.3, it was found that bismuth was coordinated with six selenium atoms and there were significant selenium vacancies. With an increase in bismuth selenide concentration, the dissolution pattern shifted to a substitutional pattern. A two fold decrease in electrical resistivity for (Bi0.98In0.02)2Te2.7Se0.3/20%Bi2Se3 composition was seen compared to (Bi0.98In0.02)2Te2.7Se0.3/5%Bi2Se3. The granular material was produced by sintering and scattering of potential barrier, a thermal process that increases the Seebeck coefficient. A 200% increase was observed in thermopower for (Bi0.98In0.02)2Te2.7Se0.3/20%Bi2Se3 compared to (Bi0.98In0.02)2Te2.7Se0.3/5%Bi2Se3 compound. [ABSTRACT FROM AUTHOR]

This article presents the results of a study of the electrochemical properties of cathodes based on polycrystalline samples of Na3Fe2(PO4)3 obtained by solid-phase synthesis and hot pressing. Factors affecting the electrochemical properties of cathodes based on Na3Fe2(PO4)3 obtained by solid-phase synthesis, hot pressing, and sol-gel are established. The prospects of using Na3Fe2(PO4)3 as a cathode material in sodium-ion batteries and the expediency of further modification of this compound in order to improve its electrochemical properties are substantiated.

Scattering of elastic waves by an anisotropic sphere with cubic symmetry inside an isotropic medium is studied. The waves in the isotropic surrounding are expanded in the spherical vector wave functions. Inside the sphere, the elastodynamic equations are first transformed to spherical coordinates and the displacement field is expanded in terms of the vector spherical harmonics in the angular directions and a power series in the radial direction. The governing equations inside the sphere give recursion relations among the expansion coefficients in the power series. The boundary conditions on the sphere then determine the expansion coefficients of the scattered wave. This determines the transition (T) matrix elements which are calculated explicitly to the leading order for low frequencies. Using the theory of Foldy, the T matrix elements of a single sphere are used to study attenuation and phase velocity of polycrystalline materials with cubic symmetry, explicitly for low frequencies and numerically for intermediate frequencies. Numerical comparisons of the present method with previously published results and recent finite element method (FEM) results show a good correspondence for low and intermediate frequencies. The present approach shows a better agreement with FEM for strongly anisotropic materials in comparison with other published methods. [ABSTRACT FROM AUTHOR]

The mechanical behavior of a magnesium alloy E-form under bending was investigated using the elasto-visco-plastic polycrystal model (ΔEVPSC) and its finite element (FE) implementation (ΔEVPSC-FE) developed in Jeong et al. and Jeong and Tomé. The crystallographic orientation distribution (COD) obtained from X-ray diffraction was used to represent the initial texture, and the Voce hardening parameters were calibrated by fitting the uniaxial tension and the compression flow stress curves. A quasi-static FE analysis of a miniaturized V-bending operation was conducted using the ΔEVPSC-FE model. The bending induced an inhomogeneous stress response along the through-thickness and the lateral directions, which was well captured by the model. Moreover, the predictive capability of the model was validated by comparing with various experimental results such as (1) force vs. displacement curves; (2) the through-thickness variations in the twin volume fraction; and (3) the changes in crystallographic texture as a function of displacement. Additional bending simulation was performed using an isotropic texture, the result of which suggests that the potential improvement in bendability of the magnesium alloy is attainable by weakening the initial texture. Moreover, the simulation results imply that the crystallographic texture, which may affect the twin activation across the thickness direction, plays a significant role in the shifting direction of the neutral layer. [ABSTRACT FROM AUTHOR]

The computational simulation of the rolling process of the polycrystalline metal plate is performed using the second-order homogenization finite element (FE) method. The dynamically updated boundary condition (BC), which can describe the relative slip displacement under counter-friction force, is introduced to reproduce the progress of nodal displacement and force BCs during the rolling process. To directly solve the displacement under the BC accompanying friction force, the components of the stiffness matrix constructed by the macroscopic FE structure are edited using the friction coefficient and the contact angle. The elasto-viscoplastic mechanical behavior of the microscopic polycrystalline structure is described by the conventional crystalline plasticity FE method, and the relative scale-depended micro- to macroscopic FE model is established using the second-order homogenization method. The computational simulations of the rolling process with different friction coefficients, rolling radii, compression ratios, and grain sizes were performed using the established FE model. The macroscopic computational results could represent the fundamental mechanical behaviors of the rolling process, e.g., reduction of the plate thickness, increase and decrease in the rolling force owing to changes in the contact area, tensile and compression stresses at the inlet and outlet areas of rolling, X-shaped local deformation band beneath the work roll, increase in the rolling load owing to the friction coefficient, work roll radius, and compression ratio. Furthermore, the microscopic computational results clarified that nonuniform deformation in the polycrystalline structure changes depending on the macroscopic position, and the nonuniformity increases with the compression ratio. The microstructure located at the upper area of the rolled material experiences a two-stage deformation characterized by the contact angle while such a two-stage deformation is not observed in the microstructure located inner area of the rolled material.

A physics-based model on polarization switching in ferroelectric polycrystalline films is proposed. The calculation results by the model agree well with experimental results regarding dynamic operations of ferroelectric-gate field-effect transistors (FeFETs). In the model, an angle θ for each grain in the ferroelectric polycrystal is defined, where θ is the angle between the spontaneous polarization and the film normal direction. Under a constant electric field for a single-crystal film with θ = 0, phenomena regarding polarization domain nucleation and wall propagation are well described by the Kolmogorov–Avrami–Ishibashi theory. Since the electric fields are time-dependent in FeFET operations and the θ values are distributed in the polycrystalline film, the model in this paper forms an extended Kolmogorov–Avrami–Ishibashi (EKAI) model. Under a low electric field, the nucleation and domain propagation proceed according to thermally activated processes, meaning that switching the time scale of a grain with the angle θ is proportional to an exponential form as exp(const./Ezcosθ) [Ez: the film-normal electric field]. Wide θ distribution makes the time response quite broad even on the logarithmic scale, which relates well with the broad switching time experimentally shown by FeFETs. The EKAI model is physics based and need not assume non-physical distribution functions in it.

A new algorithm named PolyCISAMR is introduced to automatically generate high-fidelity conforming finite element (FE) meshes for two-dimensional polycrystalline microstructures. PolyCISAMR extends the capabilities of the Conforming to Interface Structured Adaptive Mesh Refinement (CISAMR) algorithm, which transforms a structured grid overlaid on the domain geometry into a high-quality conforming mesh. The PolyCISAMR approach uses a segregated meshing strategy, where CISAMR is used to discretize each grain independently and the resulting matching meshes are merged to form the final FE model. In addition, this article presents a set of integrated algorithms for processing low-resolution images of a polycrystal, reconstructed using DREAM.3D software (Version 6.5.121), to generate NURBS characterizations for each grain prior to mesh generation. Example problems demonstrate the effectiveness of PolyCISAMR in creating high-quality meshes for various polycrystalline metallic microstructures along with corresponding crystal plasticity finite element (CPFE) simulations.

The strength $ σ_{y}(D)$ of a polycrystal can decrease or increase with the grain diameter $D$, i.e., the famous Hall-Petch (HP) and inverse-Hall-Petch (IHP) behaviors, respectively. However, $ σ_{y}(D)$ under thick grain boundaries (GBs) (i.e., GB thickness $l>1$ particle) and $ σ_{y}(l)$ have rarely been explored. Here we measure them by systematically varying $D$ and $l$ of two-dimensional glass-crystal composites in simulations. We demonstrate that increasing $l$ and decreasing $D$ have similar effects on reducing dislocation motions and promoting GB deformations. Consequently, the classical HP-IHP behaviors of $ σ_{y}(D,l=1)$ and our generalized HP-IHP behaviors of $ σ_{y}(D,l)$ share similar mechanisms and can be unified as $ σ_{y}$ ($A_\textrm{GB}/A_\textrm{tot}$), where $A_\textrm{GB}/A_\textrm{tot}$ is the fraction of the amorphous region. The results reveal a way to exceed the maximum strength of normal polycrystals. The generalized HP-IHP behaviors of $ σ_{y}(D,l)$ should be similar in 2D and 3D, except that the HP effect in 3D is stronger.

The present paper studies mathematical models for representing, imaging, and analyzing polycrystalline materials. We introduce various techniques for converting grain maps into diagram or tessellation representations that rely on constrained clustering. In particular, we show how to significantly accelerate the computation of generalized balanced power diagrams and how to extend it to allow for optimization over all relevant parameters. A comparison of the accuracy of the proposed approaches is given based on a three-dimensional real-world data set of 339\times 339\times 599 voxels. [ABSTRACT FROM AUTHOR]

The current state of research on the use of CVD diamonds in diamond tools is reviewed. Features of single crystal and polycrystalline CVD diamonds and CVD diamond films are shown. Their comparative properties are given. Their structure and the peculiarities of processing their surfaces are shown. Technological features of the preparation of diamond tools with a working layer of CVD diamonds and the use of such tools are discussed. Samples of polycrystalline CVD diamonds for the dressing tool and features of their application in the dressing rollers are shown. [ABSTRACT FROM AUTHOR]

Nickel–cobalt alloys were prepared by alloy electrodeposition with a sulfamate bath, and the mechanical properties on the micro-scale were evaluated for the application as micro-components in miniaturized electronic devices. Nickel bromide and a commercially available surface brightener were used as the additives. The cobalt content increased from 21.5 to 60.1 at.% after addition of nickel bromide into the bath, and the grain size refined from 21.1 to 13.2 nm when the surface brightener was used. The mechanical properties on the micro-scale were evaluated by micro-compression test using micro-pillar type specimens fabricated by a focused ion beam system to take the sample size effect into consideration. The yield strength of the nickel–cobalt alloy having an average grain size at 13.9 nm and cobalt content of 66.6 at.% reached 2.37 GPa, revealing influences from the sample size, grain boundary strengthening, and solid solution strengthening effects.

The influence of graphene layers and crystal structure types on the nanoindentation reinforcement mechanism of Al 0.3 CoCrFeNi high-entropy alloy/graphene (HEA/Gp) composite materials was studied using molecular dynamics (MD) simulations. The results indicate that the influence of graphene layers on composite materials is related to the position of the indenter. Before the indenter contacts the graphene layer, some dislocations are absorbed by the graphene, unable to form dislocation cells and dislocation locks to hinder the deformation of the matrix, resulting in the hardness of the composite material being lower than that of the HEA matrix. After the indentation contacts the graphene layer, dislocations can penetrate the graphene to form a high-density dislocation cell. Due to graphene's excellent deformation resistance, the composite material's load-bearing capacity is much greater than that of the HEA matrix. In addition, stress propagates along the grain boundaries in polycrystalline and twinned polycrystalline structures. Grain boundaries decrease the material strength, while twinned boundaries can refine grain size and enhance grain stability. Additionally, composite materials' elastic recovery increases first and then decreases with the increase in graphene layers and twinning. The hardness of the material shows an anomalous phenomenon about grain size following a Hall-Petch relationship. When the angle between graphene layers is 0, the stress distribution inside the material is most uniform. • The change in hardness and mechanism of composite materials is studied before and after contact with the indenter and graphene. • Grain boundaries reduce the material strength, while twin boundaries can refine the grains and improve grain stability. • The influence of graphene layers, grain size, twin crystal number, and interlayer angles of graphene on composite materials is being studied. • After loading and unloading pressure, the change of the C-C bond was analyzed. [ABSTRACT FROM AUTHOR]

This work presents two methods to improve the understanding of the mechanical behavior of nanocrystalline thin films. Firstly, a simple two-phase model is proposed to explain the inverse Hall–Petch effect. The model suggests that the nanocrystalline material consists of the grain-boundary and the grain interior with different mechanical properties. Secondly, a computational method is developed to create more realistic grain boundaries in simulations of polycrystals. Traditionally created grain boundaries by Voronoi tessellation are too dense and do not accurately reflect the reality and the experimental results. The strength of the nanocrystalline aluminum thin film is simulated using molecular dynamics. The grain size dependence of the elastic modulus, ultimate tensile stress, and engineering yield strength is demonstrated. The experimental values of modulus and strength are approximately 6 times smaller probably due to the presence of porosity in the real sample. An approach is developed to introduce porosity in the simulated samples at the grain boundaries and in the grain interior to reduce this discrepancy. The modeled value of modulus for a grain size of 40 nm without porosity is 67 GPa, whereas, with 50% grain-boundary porosity and 20% intra-granular porosity it is 30 GPa. For the ultimate tensile strength, we get 3 GPa and 1.4 GPa for samples without porosity and with porosity, respectively. The simulated values of modulus with porosity are still 4 times higher and the values of strength are about 2 times higher than the experimental ones. The amount of porosity in our method can be adjusted to fit the experimental values; however, high values of porosity cause the mechanical instability of the simulated samples. [Display omitted] [ABSTRACT FROM AUTHOR]

Schwarz crystals with uniformly distributed twins enclosed by general grain boundaries (GBs) resembling triply minimal-surfaces were observed in high stacking fault energy metal Pt which is believed not readily to twin. By refining the grains of pure Pt from 140 μm to several nanometers via plastic deformation technique, deformation twins were found to emerge numerously and the structural morphologies of Schwarz crystals can be identified at grain sizes below 4 nm. Both experiments and atomistic simulations suggest that Pt Schwarz crystals are thermally stable at temperatures approaching the thermal equilibrium melting point. The measured room temperature microhardness as a function of grain size, on the other hand, may increase monotonically up to 12.9 GPa, revealing a sustained Hall-Petch relationship. The observed outstanding mechanical stabilities can be attributed to that, regardless of the critical twin size and the stacking fault energy of the material, the plastic deformation at the grain size limit is solely limited by twinning and both the nucleation and bowing-out of twinning partial dislocations from GB sources are notoriously difficult according to simulations and theory. [Display omitted] [ABSTRACT FROM AUTHOR]

The microstructural evolution of a commercially pure copper specimen deformed by uniaxial tension has been studied using electron backscatter diffraction (EBSD). In the specimen deformed up to fracture, some areas (in the neck) corresponding to various strain degrees were examined. This allowed us to study the microstructure obtained for strain degrees in the range from 0,45 to 1,15 on the single sample. A texture consisting of two components with prevailing orientations of [100] and [111] directions, parallel to the tensile axis, formed concurrently with the deformation microstructure. The grains of the [111] component were shown to retain rather uniform orientation at strain degrees of about 1. At the same time, the grains of the [100] component subdivided gradually into highly disoriented fragments. The obtained results were discussed in terms of polycrystalline material micromechanics.

Transparent yttrium aluminum garnet (YAG) ceramics are mostly sintered under vacuum to favor pore closure. However, this may conceal the origin of microstructural defects, complicating process optimization. We describe a useful approach to understand the origin of defects in transparent YAG ceramics: reactive sintering was performed in air at a moderate temperature for a short time. The resulting microstructure allowed to understand the origin of defects in corresponding vacuum-sintered specimens. The porosity of air sintered samples could be related to the presence of aggregates of starting oxide particles, which eventually under vacuum react to form YAG, but leave behind pores. [ABSTRACT FROM AUTHOR]

Reports on unique properties achieved with high-entropy alloys have motivated the application of the multicomponent approach to oxide materials. We have applied this methodology to an alumina-based spinel oxide, resulting in the synthesis of polycrystalline (Mg1/5Ni1/5Co1/5Cu1/5Zn1/5)Al2O4. Samples were made by the polymeric steric entrapment technique and uniaxially hot-pressed to obtain dense pellets. Resonant ultrasound spectroscopy was used to evaluate the elastic behavior, allowing for a direct comparison of the mechanical properties of the multicomponent spinel to those of traditional MgAl2O4. High-temperature X-ray diffraction was used to investigate the high-temperature phase stability and thermal expansion behavior of (Mg1/5Ni1/5Co1/5Cu1/5Zn1/5)Al2O4. [ABSTRACT FROM AUTHOR]

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This paper uses three-dimensional grain-scale finite-element (FE) simulations to appraise the classical scattering theory of plane longitudinal wave propagation in untextured polycrystals with statistically equiaxed grains belonging to the seven crystal symmetries. As revealed from the results of 10 390 materials, the classical theory has a linear relationship with the elastic scattering factor at the quasi-static velocity limit, whereas the reference FE and self-consistent (SC) results generally exhibit a quadratic relationship. As supported by the results of 90 materials, such order difference also extends to the attenuation and phase velocity, leading to larger differences between the classical theory and the FE results for more strongly scattering materials. Alternatively, two approximate models are proposed to achieve more accurate calculations by including an additional quadratic term. One model uses quadratic coefficients from quasi-static SC velocity fits and is thus symmetry-specific, while the other uses theoretically determined coefficients and is valid for any individual material. These simple models generally deliver more accurate attenuation and phase velocity (particularly the second model) than the classical theory, especially for strongly scattering materials. However, the models are invalid for the attenuation of materials with negative quadratic coefficients. This article is part of the theme issue 'Wave generation and transmission in multi-scale complex media and structured metamaterials (part 1)'. [ABSTRACT FROM AUTHOR]

Silicon carbide has offered a greater impact on the composite and intermetallic industries, owed its superior material features. But its material features are entirely depended on the existence of better ambient temperature and material defects. In this current study, the impact of grain size (4.2 nm, 4.8 nm and 5.7 nm), temperature (300 K, 500 K and 700 K) and a fraction of point defects such as vacancies (0%, 3%, 6% and 9%) on the tensile performance of silicon carbide (SiC) has been investigated through the molecular dynamics method. Through the above study, it is found that structural and microstructural transformation through the diffusion mechanism plays a greater impact over the material behavior of silicon carbide monolithic nano polycrystal and additionally, it is quantified that the fraction of point defects offers a greater influence over the material features followed by the grain size and temperature. Moreover, the radial distribution function analysis has been confirmed the structural transformation behavior during tensile deformation. [ABSTRACT FROM AUTHOR]

Single-crystal and polycrystalline structures are the two main structural forms of the Ni-rich layered cathode for lithium-ion batteries. The structural difference is closely related to the electrochemical performance and thermal stability, but its internal mechanism is unclear and is worthy of further exploration. In this study, both polycrystalline and single-crystal LiNi 0.83 Co 0.12 Mn 0.05 O 2 cathodes were prepared by adjusting the calcination temperature and mechanical post-treatment, respectively. Systematic comparisons were made to assess the effects of different grain structures on the electrochemical performance and thermal stability. The study revealed the superior thermal stability of monocrystalline cathodes, attributing it to oxygen vacancies and phase transitions. From the perspective of grain boundaries, it was demonstrated that the diffusion of oxygen vacancies and the reduction of Ni in polycrystalline cathodes exhibit anisotropy. This research elucidates the origins of the superior thermal stability of monocrystalline cathodes in lithium-ion batteries, providing valuable insights into battery material design.

In this research, the structure parameters, conducting and dielectric properties of Na3Fe2(PO4)3 and Na2FePO4F polycrystals were studied obtained by solid-phase synthesis. The phase transition temperatures, conducting and dielectric parameters of Na3Fe2(PO4)3 and Na2FePO4F polycrystals were refined. A comparative evaluation of the conductive properties of Na3Fe2(PO4)3 and Na2FePO4F polycrystals is given in this article. The prospects of using of Na3Fe2(PO4)3 and Na2FePO4F are justified as electrode materials in sodium ion batteries.