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This study presents the successful synthesis of Sr2Ta2O7 with a pyrochlore crystal structure, which was previously unreported. Traditionally, Sr2Ta2O7 is synthesized in an orthorhombic layered perovskite‐type structure using traditional solid‐state reaction and batch‐type subcritical hydrothermal methods. Here, we utilize a continuous‐flow supercritical hydrothermal method, a technique primarily applied for nanoparticle synthesis and minimally explored for the synthesis of metastable crystals. Through detailed evaluations employing X‐ray diffraction and scanning electron microscopy, we confirmed the synthesis of the pyrochlore phase, characterized by particles with a diameter of less than 100 nm, synthesized at 633 K. Notably, the synthesized pyrochlore structure demonstrated remarkable stability, even after thermal treatment at 773 K for 1 h. Pyrochlore Sr2Ta2O7 stands out as a rare exception to the traditional tolerance factor approach among 278 known A2B2O7 compositions. Systematic evaluation of formation energies through first‐principles calculations revealed that the pyrochlore Sr2Ta2O7 synthesized in this study is located 0.06 eV/atom above the convex hull. This achievement underscores the potential of the continuous‐flow supercritical hydrothermal method in automating the exploration and discovery of novel crystal structures, suggesting a systematic pathway for advancing the field of material synthesis. [ABSTRACT FROM AUTHOR]

Statistical distributions of the elastic strain and stress tensor components in the grains of polycrystalline materials are necessary to calculate the probabilities of various local critical events, such as damage and others, which are of random origin due to the stochastic grain structure. Many experimental and computational studies suggest that these distributions can be approximated by a normal distribution. The normal distribution parameters are determined from histogram-like plots obtained experimentally or by computer simulation. Most published histogram distributions are highly skewed, in contrast to the normal distribution. Here we present a new direct calculation method for the probability densities of the elastic strain tensor components. The method uses an integral equation for strains in heterogeneous solids, which reduces the solution of the boundary value problem of polycrystal deformation to the sum of solutions of some problems for neighboring grains. The focus is on the influence of random grain interactions on the strain distribution. Calculations are carried out for polycrystals with different elastic symmetries and degrees of grain anisotropy. All probability densities are finite, asymmetric, and noticeably different from Gaussian ones. It is shown that very few particularly located neighboring grains (of dozens) have a much greater effect on the distribution pattern and limiting values of the strain tensor components than all the others. [ABSTRACT FROM AUTHOR]

The application of machine learning in materials science has yielded several benefits, including the prediction of physical properties and the improvement of experimental efficiency. However, with complex models, such as convolutional neural networks (CNN), learning has become a black box, from which no universal physical knowledge can be obtained. In this study, a highly accurate prediction of the electrical properties of polycrystalline semiconductor thin films is achieved by learning multichannel CNN models from electron backscattering diffraction (EBSD) data, that is band contrasts, grain boundaries, and inverse pole figures. In addition, it examines how the CNN model learned the correlation between the crystallinity, grain boundaries, crystallographic orientation, and carrier mobility by polarizing certain EBSD data and checking the predicted changes in carrier mobility. Physical parameters affecting carrier mobility can be extracted, which is challenging via human image recognition. The methods proposed in this study will not only enable the prediction of electrical properties from EBSD data for all materials but also will contribute to the discovery of complex physical phenomena beyond the limits of human analysis. [ABSTRACT FROM AUTHOR]

The effective macroscopic behaviour of a material is a manifestation of the underlying microstructure and microscale processes. This renders the generation of highly accurate digital microstructure twins indispensable for multiscale simulations. Mosaic is a Python-based, open-source software tool designed to address the challenge of incorporating non-planar, periodic microstructures generated by the software Neper into simulations that require periodic boundary conditions. Mosaic transforms these complex microstructures into rectilinear periodic equivalents and, additionally, makes it possible to account for material interfaces such as grain and phase boundaries. This transformation enables continuous integration with various simulation tools and workflows, facilitating accurate and efficient simulations of the effective material response.

Calculating the elastic and mechanical characteristics of non‐crystalline solids can be challenging due to the high computational cost of ab initio methods and the low accuracy of empirical potentials. This paper proposes a computational technique for efficient calculations of mechanical properties of polycrystals, composites, and multi‐phase systems from atomistic simulations with high accuracy and reasonable computational cost. The calculated elastic moduli of polycrystalline diamond and their dependence on grain size are determined using a developed approach based on actively learned machine learning interatomic potentials (MLIPs). These potentials are trained on local fragments of the polycrystalline system, and ab initio calculations are used to compute forces, stresses, and energies. This technique allows researchers to perform extensive calculations of the mechanical properties of complex solids with different compositions and structures, achieving high accuracy and facilitating the transition from ideal (single crystal) systems to more realistic ones. [ABSTRACT FROM AUTHOR]

X‐ray Laue microdiffraction aims to characterize microstructural and mechanical fields in polycrystalline specimens at the sub‐micrometre scale with a strain resolution of ∼10−4. Here, a new and unique Laue microdiffraction setup and alignment procedure is presented, allowing measurements at temperatures as high as 1500 K, with the objective to extend the technique for the study of crystalline phase transitions and associated strain‐field evolution that occur at high temperatures. A method is provided to measure the real temperature encountered by the specimen, which can be critical for precise phase‐transition studies, as well as a strategy to calibrate the setup geometry to account for the sample and furnace dilation using a standard α‐alumina single crystal. A first application to phase transitions in a polycrystalline specimen of pure zirconia is provided as an illustrative example. [ABSTRACT FROM AUTHOR]

Abstract The application of machine learning in materials science has yielded several benefits, including the prediction of physical properties and the improvement of experimental efficiency. However, with complex models, such as convolutional neural networks (CNN), learning has become a black box, from which no universal physical knowledge can be obtained. In this study, a highly accurate prediction of the electrical properties of polycrystalline semiconductor thin films is achieved by learning multichannel CNN models from electron backscattering diffraction (EBSD) data, that is band contrasts, grain boundaries, and inverse pole figures. In addition, it examines how the CNN model learned the correlation between the crystallinity, grain boundaries, crystallographic orientation, and carrier mobility by polarizing certain EBSD data and checking the predicted changes in carrier mobility. Physical parameters affecting carrier mobility can be extracted, which is challenging via human image recognition. The methods proposed in this study will not only enable the prediction of electrical properties from EBSD data for all materials but also will contribute to the discovery of complex physical phenomena beyond the limits of human analysis.

In the present study, density functional theory is used to conduct an in-depth investigation of the physicochemical features of the perovskite XCuH 3 (X = Ca and Sr). The CaCuH 3 and SrCuH 3 , with lattice parameters of 3.66 Å and 3.77 Å, are synthesizable and thermodynamically stable, according to structural simulations. Analysis of the electronic band structure (0 eV) and density of states (DOS) shows that XCuH 3 (X = Ca and Sr) perovskites exhibit metallic behaviour. For novel polycrystalline materials, the shear and Young's moduli as well as the Poisson's ratio are computed and the findings suggested that compounds with the formula XCuH 3 (X = Ca and Sr) are ductile. Hydrogen storage qualities have been analyzed and it has been shown that the CaCuH 3 and SrCuH 3 have gravimetric hydrogen storage capacities of 2.85 wt% and 1.97 wt%, respectively. The SrCuH 3 has the highest Debye temperature (θ D) 344.41 K. The findings, taken as a whole, provide a practical strategy for developing innovative, potentially useful perovskite-type hydrides for hydrogen storage. • XCuH 3 (X = Ca and Sr) Perovskite type hydrides have been investigated using Density Functional Theory (DFT). • XCuH 3 (X = Ca and Sr) Perovskite type hydrides are found to be thermodynamically and mechanically stable. • Highest gravimetric hydrogen storage capacities are determined for CaFeH 3 (2.85 %). • The electronic analysis showed that both hydrides are metallic nature. • Both hydrides are ductile in nature. [ABSTRACT FROM AUTHOR]

Doping uniformity has a significant impact on crystal growth process, crystal quality and performance, so it is very important to propose and improve the preparation process of polycrystalline materials to achieve uniformly doped lithium niobate crystal growth. The synthesis of crystal polycrystalline material is one of the preparatory works before crystal growth, and also the most important step before crystal growth. The quality of crystal polycrystalline material is directly related to the quality of single crystal. Partial liquid phase method combines the advantages of solid phase method and liquid phase method, which is a superior synthesis method of polycrystalline materials. In this paper, we synthesized lithium niobate polycrystalline powder by partial liquid phase method and characterized the powder to guarantee the quality. [ABSTRACT FROM AUTHOR]

Double perovskites such as Sr2CrReO6 attract great scientific attention owing to their high Curie temperatures (TC ≥ 550 K) as well as large magnetoresistances. However, both the specific physical mechanism of high TC and magnetic ground state in Sr2CrReO6 remain ill‐defined. In order to clarify and understand these issues, we studied its critical phase transition characteristics using critical behavior analysis. We found that the obtained critical exponents (β = 1.115 and γ = 2.224) are quite different from any traditional universality class. The abnormal critical behavior implies that at the quantum critical point, Sr2CrReO6 exists a strong competition among several magnetic interactions. By analyzing their effective critical exponents, we show that the double perovskite Sr2CrReO6 is really an ordered and homogeneous ferromagnet. With the help of Takahashi's theory, the nature of ferromagnetism in Sr2CrReO6 is confirmed to be localized instead of itinerant. The results of this research will provide new insights into the origins of high TC as well as the magnetic ground state in this double perovskite. [ABSTRACT FROM AUTHOR]

Double perovskites such as Sr2CrReO6 attract great scientific attention owing to their high Curie temperatures (TC ≥ 550 K) as well as large magnetoresistances. However, both the specific physical mechanism of high TC and magnetic ground state in Sr2CrReO6 remain ill‐defined. In order to clarify and understand these issues, we studied its critical phase transition characteristics using critical behavior analysis. We found that the obtained critical exponents (β = 1.115 and γ = 2.224) are quite different from any traditional universality class. The abnormal critical behavior implies that at the quantum critical point, Sr2CrReO6 exists a strong competition among several magnetic interactions. By analyzing their effective critical exponents, we show that the double perovskite Sr2CrReO6 is really an ordered and homogeneous ferromagnet. With the help of Takahashi's theory, the nature of ferromagnetism in Sr2CrReO6 is confirmed to be localized instead of itinerant. The results of this research will provide new insights into the origins of high TC as well as the magnetic ground state in this double perovskite. [ABSTRACT FROM AUTHOR]

X-ray diffraction techniques are widely used to estimate stresses within polycrystalline materials. The application of these techniques requires the knowledge of the X-ray elastic constants relating the lattice strains to the stress state. Different analytical methods have been proposed to evaluate the X-ray elastic constants from the single-crystal elastic constants. For a given material, such methods provide the bulk X-ray elastic constants but they do not consider the role of free surfaces. However, for many practical applications of X-ray diffraction techniques, the penetration depth of X-rays is the same order of magnitude as the grain size, which means that the influence of the free surface on X-ray elastic constants cannot be excluded. In the present work, a numerical procedure is proposed to evaluate the surface and bulk X-ray elastic constants of polycrystalline materials. While the former correspond to the situation where the penetration is infinitely small in comparison with the grain size, the latter are representative of an infinite penetration depth with no free-surface effect. According to numerical results, the difference between surface and bulk X-ray elastic constants is important for strongly anisotropic crystals. Also, it is possible to propose a relation that allows evaluating X-ray elastic constants as a function of the ratio between the penetration depth and the average grain size. The corresponding parameters of such a relation are provided here for many engineering materials. [ABSTRACT FROM AUTHOR]

Different from focusing on grain boundary upper surface in plane X–Y, a unique approach of nanorobot‐based nondestructive characterization of grain boundary Z‐directional lateral surface within bulk ZnO ceramic can be creatively developed under scanning electron microscope (SEM). By rolling‐over bulk ZnO, two‐dimensional profiles and grain boundaries in Z‐directional lateral surfaces have been imaged in plane Y–Z and individually electrically characterized nondestructively. Experiments demonstrate that it is feasible to realize nondestructive characterization of grain boundary Z‐directional lateral surface structures and electrical properties using nanorobot combined with SEM. Relative height differences between grain boundaries within Z‐directional lateral surface can characterize the relative position relationships. Z‐directional lateral surface structures can further extend irregular grain boundary lengths in plane Y–Z to interpret surface effects of nonlinear electrical properties. Relative minor electrical reactive effects in grain indicate grain boundary dominate in nonlinear macroscopic electrical properties. Furtherly, it can be advanced to promote a nondestructive characterization of grain boundary. [ABSTRACT FROM AUTHOR]

The microstructure of polycrystals is known to govern the performance of structural materials. This drives the need for mechanical characterization methods capable of probing large representative volumes at the grain and sub-grain scales. In this paper, the use of in situ diffraction contrast tomography (DCT) along with far-field 3D X-ray diffraction (ff-3DXRD) at the Psiché beamline of Soleil is presented and applied to study crystal plasticity in commercially pure titanium. A tensile stress rig was modified to comply with the DCT acquisition geometry and used for in situ testing. DCT and ff-3DXRD measurements were carried out during a tensile test of a tomographic Ti specimen up to 1.1% strain. The evolution of the microstructure was analyzed in a central region of interest comprising about 2000 grains. Using the 6DTV algorithm, DCT reconstructions were successfully obtained and allowed the characterization of the evolution of lattice rotation in the entire microstructure. The results are backed up by comparisons with EBSD and DCT maps acquired at ESRF-ID11 that allowed the validation of the orientation field measurements in the bulk. Difficulties at the grain boundaries are highlighted and discussed in line with increasing plastic strain during the tensile test. Finally, a new outlook is provided on the potential of ff-3DXRD to enrich the present dataset with access to average lattice elastic strain data per grain, on the possibility of performing crystal plasticity simulations from DCT reconstructions, and ultimately on comparisons between experiments and simulations at the scale of the grain.

In this work, we develop and employ an accelerated design strategy using a machine learning algorithm to overcome the challenges for designing a new machinable glass ceramic. The trained machine learning model predicts the specific hardness value for numerous possibilities of processing conditions such as growth temperature and time. We report that the optimized growth parameters of 1200°C and 5 h achieve the highest machinability of 0.4 in the glass ceramic. Furthermore, we predicted the eight most promising candidates containing specific ratios of silicon, magnesium, aluminum, lithium, boron, potassium, barium, and oxygen. Combining machine learning with experimental data enables a systemic and rapid design of a ceramic material while capturing the underlying physics represented in the experimental data. [ABSTRACT FROM AUTHOR]

Two data evaluation concepts for X‐ray stress analysis based on energy‐dispersive diffraction on polycrystalline materials with cubic crystal structure, almost random crystallographic texture and strong single‐crystal elastic anisotropy are subjected to comparative assessment. The aim is the study of the residual stress state in hard‐to‐reach measurement points, for which the sin2ψ method is not applicable due to beam shadowing at larger sample tilting. This makes the approaches attractive for stress analysis in engineering parts with complex shapes, for example. Both approaches are based on the assumption of a biaxial stress state within the irradiated sample volume. They exploit in different ways the elastic anisotropy of individual crystallites acting at the microscopic scale and the anisotropy imposed on the material by the near‐surface stress state at the macroscopic scale. They therefore complement each other, in terms of both their preconditions and their results. The first approach is based on the evaluation of strain differences, which makes it less sensitive to variations in the strain‐free lattice parameter a0. Since it assumes a homogeneous stress state within the irradiated sample volume, it provides an average value of the in‐plane stresses. The second approach exploits the sensitivity of the lattice strain to changes in a0. Consequently, it assumes a homogeneous chemical composition but provides a stress profile within the information depth. Experimental examples from different fields in materials science, namely shot peening of austenitic steel and in situ stress analysis during welding, are presented to demonstrate the suitability of the proposed methods. [ABSTRACT FROM AUTHOR]

The microstructure of polycrystals is known to govern the performance of structural materials. This drives the need for mechanical characterization methods capable of probing large representative volumes at the grain and subgrain scales. In this paper, the use of in situ diffraction contrast tomography (DCT) along with far-field 3D X-ray diffraction (ff-3DXRD) at the Psiche' beamline of Soleil is presented and applied to study crystal plasticity in commercially pure titanium. A tensile stress rig was modified to comply with the DCT acquisition geometry and used for in situ testing. DCT and ff-3DXRD measurements were carried out during a tensile test of a tomographic Ti specimen up to 1.1% strain. The evolution of the microstructure was analyzed in a central region of interest comprising about 2000 grains. Using the 6DTV algorithm, DCT reconstructions were successfully obtained and allowed the characterization of the evolution of lattice rotation in the entire microstructure. The results are backed up by comparisons with EBSD and DCT maps acquired at ESRF-ID11 that allowed the validation of the orientation field measurements in the bulk. Difficulties at the grain boundaries are highlighted and discussed in line with increasing plastic strain during the tensile test. Finally, a new outlook is provided on the potential of ff-3DXRD to enrich the present dataset with access to average lattice elastic strain data per grain, on the possibility of performing crystal plasticity simulations from DCT reconstructions, and ultimately on comparisons between experiments and simulations at the scale of the grain. [ABSTRACT FROM AUTHOR]

Polycrystalline zinc selenide (ZnSe) and Cr2+ or Fe2+ doped ZnSe are key optical elements in mid-infrared laser systems. The laser-induced damage of the optical elements is the limiting factor for increasing the power and pulse energy of the lasers. In the present work, the optical damage of the ZnSe, Cr2+:ZnSe, and Fe2+:ZnSe samples induced by a repetitively pulsed Ho3+:YAG laser at 2091 nm was studied. The probability of the optical damage and the laser-induced damage threshold (LIDT) were determined for the samples manufactured using different processing techniques. The highest LIDT was found in ZnSe samples annealed in an argon atmosphere. It was also found that the samples annealed in a zinc atmosphere or with hot isostatic pressing resulted in a decrease in the LIDT. The Cr2+-doped ZnSe had the lowest LIDT at 2.1 µm compared to Fe2+-doped or undoped ZnSe. The LIDT fluence of all tested ZnSe samples decreased with the increase in the pulse repetition rate and the exposure duration. The results obtained may be used to improve the treatment procedures of ZnSe, Cr2+:ZnSe, and Fe2+:ZnSe polycrystals to further increase their LIDT.

An image processing technique is proposed to measure the deformation of polycrystalline materials based on correlating the grains in reference and deformed SEM images. The advantage of this technique compared to the conventional subset‐based Digital Image Correlation (DIC) is that it can be applied when speckle patterning is not efficient or when studying boundary‐related mechanics is the objective. The technique is based on correlating grains by defining their boundaries rather than just subsets of image pixels. It reveals the anisotropy inherent in the polycrystals since it allows the analysis to specify each grain separately without averaging the results. The technique is applied by detecting the approximate grain boundaries edges and then refining their location with high accuracy. The correlation is performed between points calculated from each grain in the reference and deformed images as a Point Set Registration (PSR) problem. Finally, the displacements and strains are calculated from the resulting transformation matrix. A benchmark problem was developed to discuss the error over a strain range of 0.02 to 0.2 and showed that the resulting strains are reasonably accurate. Also, an in situ experiment was conducted to demonstrate the implementation of the technique using a specimen with fine‐grained Zirconia polycrystals. The technique successfully revealed the crack tip plastic zone, and strain mismatch between grains. [ABSTRACT FROM AUTHOR]

A von Mises criterion for compatible deformation states that five independent slip systems must operate for polycrystals to deform uniformly and without failure at the grain boundaries, which is supported by the Taylor–Bishop–Hill theory or simply the Taylor model, defining the laws of plastic deformation of polycrystalline aggregates and being one of the key cornerstones of crystal plasticity theory. However, the criterion has fundamental flaws as it is based on an unfounded correlation between phenomenological material flow behaviour in continuum mechanics and crystal structure dependent dislocation slip, and there has been no experimental evidence to show simultaneous operation of five independent slip systems. In this paper, the Von Mises criterion and the Taylor model are revisited and examined critically, and the fundamental issues related to the requirement of independent slip systems for compatible deformation and the selection of the active slip systems are addressed. Detailed analysis is performed of the stress state that eliminates the possibility of the simultaneous operation of five independent slip systems, and of the relative displacement vector due to the dislocation slip which defines the quantity of the strain that can be expressed by a strain tensor, instead of individual strain components. Discussions are made to demonstrate that although three linearly independent slip systems are essentially sufficient for compatible deformation, one slip system, being selected according to Schmidt law, dominates at a time in a characteristic domain as deformation accommodation occurs between grains or characteristic domains rather than at each point. [ABSTRACT FROM AUTHOR]

A new ferroelectric solid solution (1 − x)PbTiO3–xBi(Li1/2Nb1/2)O3 has been explored to develop high‐temperature piezoelectric material. An interesting observation has been found regarding its Curie point (TC) and tetragonal lattice strain (c/a − 1). With increasing composition (x), the Curie point (TC) decreases up to x = 0.10 and thereafter remains constant. In concurrence with the TC, the tetragonal lattice strain (c/a − 1) follows a similar trend. Neutron powder diffraction analysis suggests this anomalous behavior is due to the robust off‐centering characteristic of the Bi+3 ion 6S2 lone pair effect at the A‐site compared to ions at B‐site. [ABSTRACT FROM AUTHOR]

To evaluate the radiation tolerance of polycrystalline materials, the damage effects of Fe and W as typical body-centered cubic metals under uniform irradiation are studied by multi-scale models. A guiding descriptor, the absorption bias (the ratio of the absorption abilities of grain boundaries (GBs) to interstitials (I) and vacancies (V)), is proposed to reflect the radiation tolerance of metals with different grain sizes. Low absorption bias promotes defects annihilation through enhancing I-V recombination and optimally tuning its competition with GB absorption. Polycrystalline metals possess high radiation resistant performance with low absorption bias regulated by grain size and temperature. Furthermore, by comprehensively considering the mechanical property, thermal stability, and radiation tolerance described by absorption bias, nano-crystals are recommended for Fe-based structural materials but coarse-grained crystals for W-based plasma-facing materials. This work reevaluates the radiation tolerance of polycrystalline metals, resulting in new strategies for designing structural materials in nuclear devices through manipulating grain sizes. [ABSTRACT FROM AUTHOR]

The microstructure of metals and foams can be effectively modelled with anisotropic power diagrams (APDs), which provide control over the shape of individual grains. One major obstacle to the wider adoption of APDs is the computational cost that is associated with their generation. We propose a novel approach to generate APDs with prescribed statistical properties, including fine control over the size of individual grains. To this end, we rely on fast optimal transport algorithms that stream well on Graphics Processing Units (GPU) and handle non-uniform, anisotropic distance functions. This allows us to find large APDs that best fit experimental data and generate synthetic high-resolution microstructures in (tens of) seconds. This unlocks their use for computational homogenisation, which is especially relevant to machine learning methods that require the generation of large collections of representative microstructures as training data. The paper is accompanied by a Python library, PyAPD , which is freely available at: www.github.com/mbuze/PyAPD. [Display omitted] • Synthetic microstructure generation using anisotropic power diagrams (APDs). • Fast algorithm for generating APDs with grains of given volumes. • Tools: Anisotropic power diagrams and GPU-accelerated optimal transport techniques. • A three-orders-of-magnitude speed-up vs CPU methods. • A practical tool for generating large data sets for virtual design of new materials. [ABSTRACT FROM AUTHOR]

In this work, a grain boundary formulation for intergranular and transgranular micro-cracking in three-dimensional polycrystalline aggregates is presented. The formulation is based on the displacement and stress boundary integral equations of solid mechanics and it has the advantage of expressing the polycrystalline problem in terms of grain boundary variables only. The individual grains within the polycrystalline morphology are modelled as generally anisotropic linear elastic domains with random spatial orientation. Transgranular micro-cracking is assumed to occur along specific cleavage planes, whose orientation in space within the grains depend upon the crystallographic lattice. Both intergranular and transgranular micro-cracking are modelled using suitably defined cohesive laws, whose parameters characterise the behaviour of the two mechanisms. The algorithm developed to track the inter/transgranular micro-cracking history is presented and discussed. Several numerical tests involving pseudo-3D and fully 3D morphologies are performed and analysed. The presented numerical results show that the developed formulation is capable of tracking the initiation and evolution of both intergranular and transgranular cracking as well as their competition, thus providing a useful tool for the study of damage micro-mechanics.

Carrier recombination at the grain boundary (GB) interfaces greatly affects the performance of polycrystalline (pc) material-based thin-film devices. Effect of GB-orientation on minority carrier recombination in pc-materials has been investigated in the present work by developing an analytical model for GB-recombination. The developed model considers Gaussian-distributed acceptor and donor-like traps with an unequal capture-cross section of electrons and holes. The effect of GB-orientation and GB-trap density on the recombination rate and velocity has been analyzed. Two-dimensional TCAD numerical simulations have also been carried out to compare the theoretical and simulated results. Result shows that the GBs orientated along the direction of carrier flow are more effective for recombination loss as compared to those oriented in other directions. Thus, by engineering the GB-orientation, performance of pc-material-based electronic and photosensitive devices can be enhanced. Result also shows that the impact of GB-trap density becomes significant when its value lies in the range of 1011–1014 cm−2. [ABSTRACT FROM AUTHOR]

Polycrystalline zinc selenide (ZnSe) and Cr2+ or Fe2+ doped ZnSe are key optical elements in mid-infrared laser systems. The laser-induced damage of the optical elements is the limiting factor for increasing the power and pulse energy of the lasers. In the present work, the optical damage of the ZnSe, Cr2+:ZnSe, and Fe2+:ZnSe samples induced by a repetitively pulsed Ho3+:YAG laser at 2091 nm was studied. The probability of the optical damage and the laser-induced damage threshold (LIDT) were determined for the samples manufactured using different processing techniques. The highest LIDT was found in ZnSe samples annealed in an argon atmosphere. It was also found that the samples annealed in a zinc atmosphere or with hot isostatic pressing resulted in a decrease in the LIDT. The Cr2+-doped ZnSe had the lowest LIDT at 2.1 µm compared to Fe2+-doped or undoped ZnSe. The LIDT fluence of all tested ZnSe samples decreased with the increase in the pulse repetition rate and the exposure duration. The results obtained may be used to improve the treatment procedures of ZnSe, Cr2+:ZnSe, and Fe2+:ZnSe polycrystals to further increase their LIDT. [ABSTRACT FROM AUTHOR]

In this work, we propose a novel higher-order nonlocal operator method (NOM) based anisotropic phase-field approach to brittle fractures in rock-like materials and polycrystalline materials. The integral forms of the nonlocal phase-field and its corresponding mechanical model are obtained through the application of a variational principle. The implementation of the higher-order NOM is straightforward as it does not require the use of shape functions and their associated derivatives. Furthermore, the proposed method overcomes the limitation of the original nonlocal operator method, which exhibited first-order interpolation accuracy in the convergence test. The utilization of the reproducing kernel particle method is applied to obtain a nonlocal operator, enhancing both computational stability and accuracy. Moreover, the present method allows for the simulation of crack propagation patterns, both intergranular and transgranular, in polycrystalline materials. The present method is demonstrated through the use of several numerical examples, which provide a detailed understanding of the intricate mechanisms of crack initiation, propagation, and coalescence in both rock-like and polycrystalline materials. • A novel higher-order nonlocal operator theory for the phase-field modeling of anisotropic brittle fracture is proposed. • The proposed method does not require the use of shape functions and their associated derivatives. • The nonlocal phase field model is derived using both the nonlocal operator method and the variational principle. • A 3D crack propagation in rock-like materials and polycrystalline materials is studied. [ABSTRACT FROM AUTHOR]

Crystallographic texturing of ferroelectrics is known to improve the piezoelectrics response due to the alignment of optimal grain orientations in polycrystalline materials. Using high‐energy x‐ray diffraction, a ferroelastic self‐poling effect was observed in crystallographically textured 0.68 Pb(Mg1/3Nb2/3)O3− 0.32PbTiO3 ceramic. It is shown that the BaTiO3 platelet templates used to induce crystallographic texture imposed a biaxial strain causing ferroelastic domains to re‐orient parallel to the template plate normal. In‐situ high‐energy x‐ray diffraction was then used to characterize the response mechanisms of the material with applied electric fields. The textured ceramic produced a (111) lattice strain of 0.13% in the remanent state, and a 0.16% (111) unipolar lattice strain at 2 kV/mm while the untextured ceramic had a higher (111) lattice strain of 0.18% in the remanent state and a smaller (111) unipolar lattice strain at 2 kV/mm of 0.096%. This contrast in the strain magnitudes can be linked to the self‐poling effect. A strain mechanism incorporating the self‐poling effect is proposed, furthering our understanding of how crystallographic texture impacts the piezoelectric properties and providing a pathway for engineering the self‐poling effect to further enhance material response. [ABSTRACT FROM AUTHOR]

During the vacuum hot pressing sintering process, a certain thickness of graphite foil is usually used as the isolation layer to avoid the adhesion between ceramic and graphite die. Here, the graphite foil was replaced by a platinum sheet in the sintering process. The microstructure, weak texture, and electrical properties of pressure‐sintered CaCeNbWO8 thermosensitive ceramics were investigated and compared with pressureless‐sintered ceramics. The relative densities of the pressureless‐sintered and pressure‐sintered ceramics were 79.4% and 97.0%, respectively. The tetragonal scheelite structure having space group I41/a (88) was further confirmed by Rietveld refinement. The corresponding (112) Pole Figures showed that the weak texture intensity changed from 2.32 to 3.08 mud. Results demonstrate that the improvement of the vacuum hot pressing sintering process is in favor of obtaining high stability thermosensitive ceramics, which might potentially be applied to the mass preparation of functional ceramics or high‐density ceramics. [ABSTRACT FROM AUTHOR]

Zirconium carbide (ZrC) ceramic is one of the most important and promising materials with a high melting point. However, its low diffusion coefficient affects its densification behavior, which dramatically limits its engineering application. For polycrystal ceramic materials, sintering by thermal diffusion is the most widely used method for consolidation. But in view of the difficult densification behavior of ZrC, it is necessary to develop new sintering methods together with another driving force. In the study, we reported an ultra‐high‐pressure sintering strategy to fully densify ZrC ceramic under 1.7 GPa at 1600℃. The sintered sample exhibited high density, fine grain size, excellent mechanical properties, and a large number of crystal defects, including dislocation networks and walls, which were similar to those in deformed metals. Its hardness increased to 2057.44 HV0.1 because of its unique microstructure. [ABSTRACT FROM AUTHOR]

The present paper deals with the consideration of the rate-sensitivity mechanical behavior of metallic materials, in the framework of mean field and full field homogenization approaches. We re-examine the possibility of describing properly this rate sensitivity with a simple and widely used power law expressed at the level of the slip system, and we propose a methodology to accelerate the identification of the global material constitutive law for Finite Element (FE) simulations. For such an aim, simulations of a tensile test are conducted, using a simple homogenization model (the Taylor one, used in a relaxed constraint form) and an FE code (Abaqus), both using the same single-crystal rate-dependent constitutive law. It is shown that, provided that the identification of this law is performed with care and well adapted to the examined case (rate-sensitive or insensitive materials, static and/or dynamic ranges), the simple power law can be used to simulate the macroscopic behavior of polycrystalline aggregates in a wide range of strain rate (including both static and dynamic regimes) and strain-rate sensitivity values (up the rate-insensitive limit).

The temperature dependences of the electrical conductivity σ(T), Seebeck coefficient σ(T), and heat capacity Cp(T) of polycrystalline samples of Bi2Te3, Bi2Te3+1%CuI, and Bi2Te3+1%(CuI+1/2Pb) are investigated in the temperature range below room temperature. Based on the temperature dependences of all investigated physical properties, it is discovered that phase transition occurs at 120–200 K. Investigation of single crystals shows that anomalies in the electrical resistivity (ρ(T)=1/σ(T)) occur only across the crystal growth axis (across the well‐conducting Bi–Te plane). Investigation of the low‐temperature dependence of electrical conductivity shows that all polycrystalline samples exhibit quasi‐two‐dimensional electron transport. Additionally, quasi‐two‐dimensional transport is detected in single crystals based on anisotropy analysis ρ⊥(T)/ρ‖(T):10 (where ρ‖(T) is the resistivity along the crystal growth axis, and ρ⊥(T) is resistivity across the crystal growth axis) and temperature dependence ρ(T):T2 below 50 K. The Fermi energy EF is estimated using the temperature dependence of S(T). It is discovered that an increase in EF at T > 200 K is associated with the phase transition. For single‐crystal samples, the maximum thermoelectric figure of merit ZT, as observed along the crystal growth axis, increases with doping. A maximum ZT value of ∼1.1 is observed for the Bi2Te3+1%(CuI+1/2Pb) sample at room temperature (T=300K). [ABSTRACT FROM AUTHOR]

The temperature dependences of the electrical conductivity σ(T), Seebeck coefficient σ(T), and heat capacity Cp(T) of polycrystalline samples of Bi2Te3, Bi2Te3+1%CuI, and Bi2Te3+1%(CuI+1/2Pb) are investigated in the temperature range below room temperature. Based on the temperature dependences of all investigated physical properties, it is discovered that phase transition occurs at 120–200 K. Investigation of single crystals shows that anomalies in the electrical resistivity (ρ(T)=1/σ(T)) occur only across the crystal growth axis (across the well‐conducting Bi–Te plane). Investigation of the low‐temperature dependence of electrical conductivity shows that all polycrystalline samples exhibit quasi‐two‐dimensional electron transport. Additionally, quasi‐two‐dimensional transport is detected in single crystals based on anisotropy analysis ρ⊥(T)/ρ‖(T):10 (where ρ‖(T) is the resistivity along the crystal growth axis, and ρ⊥(T) is resistivity across the crystal growth axis) and temperature dependence ρ(T):T2 below 50 K. The Fermi energy EF is estimated using the temperature dependence of S(T). It is discovered that an increase in EF at T > 200 K is associated with the phase transition. For single‐crystal samples, the maximum thermoelectric figure of merit ZT, as observed along the crystal growth axis, increases with doping. A maximum ZT value of ∼1.1 is observed for the Bi2Te3+1%(CuI+1/2Pb) sample at room temperature (T=300K). [ABSTRACT FROM AUTHOR]

This study extends the second-order attenuation (SOA) model for elastic waves in texture-free inhomogeneous cubic polycrystalline materials with equiaxed grains to textured polycrystals with ellipsoidal grains of arbitrary crystal symmetry. In term of this work, one can predict both the scattering-induced attenuation and phase velocity from Rayleigh region (wavelength >> scatter size) to geometric region (wavelength << scatter size) for an arbitrary incident wave mode (quasi-longitudinal, quasi-transverse fast or quasi-transverse slow mode) in a textured polycrystal and examine the impact of crystallographic texture on attenuation and phase velocity dispersion in the whole frequency range. The predicted attenuation results of this work also agree well with the literature on a textured stainless steel polycrystal. Furthermore, an analytical expression for quasi-static phase velocity at an arbitrary wave propagation direction in a textured polycrystal is derived from the SOA model, which can provide an alternative homogenization method for textured polycrystals based on scattering theory. Computational results using triclinic titanium polycrystals with Gaussian orientation distribution function (ODF) are also presented to demonstrate the texture effect on attenuation and phase velocity behaviors and evaluate the applicability and limitation of an existing analytical model based on the Born approximation for textured polycrystals. Finally, quasi-static phase velocities predicted by this work for a textured polycrystalline copper with generalized spherical harmonics form ODF are compared to available velocity bounds in the literature including Hashin−Shtrikman bounds, and a reasonable agreement is found between this work and the literature.

A von Mises criterion for compatible deformation states that five independent slip systems must operate for polycrystals to deform uniformly and without failure at the grain boundaries, which is supported by the Taylor–Bishop–Hill theory or simply the Taylor model, defining the laws of plastic deformation of polycrystalline aggregates and being one of the key cornerstones of crystal plasticity theory. However, the criterion has fundamental flaws as it is based on an unfounded correlation between phenomenological material flow behaviour in continuum mechanics and crystal structure dependent dislocation slip, and there has been no experimental evidence to show simultaneous operation of five independent slip systems. In this paper, the Von Mises criterion and the Taylor model are revisited and examined critically, and the fundamental issues related to the requirement of independent slip systems for compatible deformation and the selection of the active slip systems are addressed. Detailed analysis is performed of the stress state that eliminates the possibility of the simultaneous operation of five independent slip systems, and of the relative displacement vector due to the dislocation slip which defines the quantity of the strain that can be expressed by a strain tensor, instead of individual strain components. Discussions are made to demonstrate that although three linearly independent slip systems are essentially sufficient for compatible deformation, one slip system, being selected according to Schmidt law, dominates at a time in a characteristic domain as deformation accommodation occurs between grains or characteristic domains rather than at each point.

This manuscript establishes a crystal plasticity finite element (CPFE) model with large volumetric deformation for β -HMX (1,3,5,7-tetranitro-1,3,5,7-tetrazocane) energetic crystals with emphasis on the deformation twinning behavior under shock loading conditions. The CPFE model captures the nonlinear response of the monoclinic crystal through the application of large volumetric change under shock condition, dislocation slip at low and high moving speeds and mechanical twinning idealized by the twin volume fraction evolution. The twinning behavior is distinguished from dislocation slip through the decomposition of the plastic velocity gradient in which dislocation slip, twinning and slip in the twinned region are separately considered. Third-order Birch Murnaghan EOS is incorporated in the CPFE framework to describe the volumetric deformation under extreme pressure induced by explosion or impact. The results of the numerical investigations show that the twinning behavior exhibits strong orientation dependency, which becomes more evident at higher loading regime. Particle shape significantly affects the twin concentration. Peak twin volume fraction in HMX polycrystalline with regularized particle shapes is lower compared with mesostructure with realistic particle morphologies. [ABSTRACT FROM AUTHOR]

During heat treatment or mechanical processing, most polycrystalline materials experience grain growth, which significantly affects their mechanical properties. Microstructure simulation on a mesoscopic scale is an important way of studying grain growth. A key research focus of this type of method has long been how to efficiently and accurately simulate the grain growth caused by a non-uniform temperature field with temperature gradients. In this work, we propose an improved 3D Monte Carlo Potts (MCP) method to quantitatively study the relationship between non-uniform temperature fields and final grain morphologies. Properties of the aluminum alloy AA6061-T6 are used to establish a trial calculation model and to verify the algorithms with existing experimental results in literature. The detailed grain growth process of the 6061-T6 aluminum alloy under different temperature fields is then obtained, and grain morphologies at various positions are analyzed. Results indicate that while absolute temperature and duration time are the primary factors determining the final grain size, the temperature gradient also has strong influence on the grainmorphologies. The relationships between temperatures, temperature gradients and grain growth process have been established. The proposedMCP algorithm can be applied to different types of materials when the proper parameters are used. [ABSTRACT FROM AUTHOR]

• OSB-PD model for granular fracture considering arbitrary grain orientations is proposed. • Effects of grain orientations on mechanical and fracture behaviors are studied. • Transgranular and intergranular cracks considering randomness of microstructure are captured. Granular fracture holds significant implications in material mechanics. However, the previous studies in ordinary state-based peridynamic (OSB-PD) framework often neglect the internal crystalline structure of particles or only consider limited crystal orientation. To address this gap, a novel OSB-PD model for granular fracture within polycrystalline materials is proposed, in which the periodic functions are incorporated in the PD strain energy density, taking into account the inherent random orientation in cubic crystals. By comparing energy density from PD and the classical continuum mechanics, four PD material parameters are defined. Moreover, the corresponding surface correction method in the global coordinate system is also proposed. Several numerical examples including fracture analysis of polycrystalline materials are conducted to validate the effectiveness of the proposed method. The proposed ordinary state-based peridynamic model offers a fresh perspective for investigating granular fracture behaviors within polycrystalline materials. [ABSTRACT FROM AUTHOR]

This article presents a design procedure for structural health monitoring systems based on bulk wave ultrasonic sensors for structures fabricated from polycrystalline materials. When designing a monitoring system, maximum coverage per transducer is a general requirement in order for the system to be economic. For coarse-grained polycrystalline materials, monitoring is often made challenging by low signal-to-noise ratios caused by grain scattering. Therefore, when designing a monitoring system for these materials, in addition to the economic requirement, it needs to be ensured that an adequate signal-to-noise ratio can be obtained throughout the monitoring volume. This typically introduces a trade-off between volume coverage per transducer and sensitivity that must be investigated. In this article, this trade-off is studied and a methodology using signal-to-noise maps is presented to design the system, that is, choose the optimal transducer parameters and placement. First, a combined analytical and numerical approach is used to generate a signal-to-noise map. Then, the influence of various factors on signal-to-noise ratio is investigated. Finally, two representative examples, with different criteria, are given to illustrate the methodology. In one example, the full surface area of the testpiece is covered with transducers and the optimum gives the deepest coverage. The other one aims to achieve the minimum fractional surface area that has to be covered with transducers to monitor a narrow depth range far from the surface, which has a potential application in weld monitoring. Results show that the optimum is likely to be at much lower frequency than typically used in inspection, as tracking signals with time gives sensitivity gains. Experiments were carried out to illustrate that higher volume coverage can be obtained at lower frequencies. [ABSTRACT FROM AUTHOR]