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A gradient nano-grained (GNG) structure demonstrates satisfactory surface strength. However, the underlying mechanism responsible for its strengthening lacks sufficient research. To explain how gradient nano-grained structures improve surface strength in detail, large-scale parallel molecular dynamics simulations are utilized in this study to investigate the mechanical deformation behavior of BCC tungsten with varying grain sizes during spherical nanoindentation. The findings suggest that a well-designed gradient structure can promote rational plasticity and an appropriate distribution of internal atomic stress. The critical point of maximum stress and hardness is observed when the initial grain size is 4.5 nm, with an average grain size of 7.1 nm. The interaction between grain boundary slip and migration in small grains, along with the enhanced activity of grain boundary dislocations in large grains, collectively contributes to the enhancement of the strength and hardness of the GNG structure. Compared with a homogeneous nano-grained structure, the gradient nano-grained structure exhibits a more rational distribution of dislocations and stress relaxation effects to enhance strength. The present work utilizes the molecular dynamics nanoindentation method to study GNG materials, providing a methodology for investigating the surface strengthening effects of GNG structures at the atomic scale and effectively revealing potential mechanisms for resisting surface deformation in GNG structures. [ABSTRACT FROM AUTHOR]

Crystal structure, bandgap, and the changes in the charge conduction mechanisms in ceramics are interrelated, and the underlying physics unifies all these different phenomena. The experimental and theoretical evaluation of the electronic properties of the solid solution of (1 − x)BaTiO3–(x)LaFeO3 (x = 0, 0.015, 0.031, 0.062) is attempted in this work. Bandgap was observed to be tunable with La/Fe doping from 3.2 eV (x = 0) to 2.6 eV (x = 0.06), while the lattice disorder was found to increase. A theoretical assessment confirms a considerable shift of valence band maxima and conduction band minima with an introduction of additional defect states within the bandgap. Electron localization was also confirmed theoretically with doping. Such changes in the electronic properties were experimentally confirmed from dielectric/AC - conductivity/impedance spectroscopy studies. From different transportation models, hopping is a preferred mechanism in the less distorted BaTiO3. However, a large polaron tunneling process can be justified for the doped samples at lower temperatures. Only at higher temperatures, a small polaron tunneling can be justified for the doped samples. The transportation is affected by the grain boundaries as much as the grains themselves. A complete analysis using Nyquist plots reveals the competing contributions of these regions to the transportation mechanism and is correlated to the disorder/distortions in the lattice in terms of the formation of oxygen vacancies. [ABSTRACT FROM AUTHOR]

Grain boundary (GB) segregation models are derived for multi-principal element alloys (MPEAs) and high-entropy alloys (HEAs). Differing from classical models where one component is taken as a solvent and others are considered solutes, these models are referenced to the bulk composition to enable improved treatments of MPEAs and HEAs with no principal components. An ideal solution model is first formulated and solved to obtain analytical expressions that predict GB segregation and GB energy in MPEAs and HEAs. A regular solution model is further derived. The GB composition calculated using the simple analytical expression derived in this study and data from the Materials Project agrees well with a prior atomistic simulation for NbMoTaW. The simplicity of the derived analytical expressions makes them useful for not only conveniently predicting GB segregation trends in HEAs but also analyzing nascent interfacial phenomena in compositionally complex GBs. As an application example, the models are used to further derive a set of equations to elucidate an emergent concept of high-entropy grain boundaries. [ABSTRACT FROM AUTHOR]

Consistent c-axis orientation characteristics toward the direction of applied pressure of Y-type BaSrCo2Fe11AlO22 (BSCFAO-θ) were successfully prepared by the strategy of hot pressing. The samples' magnetoelectric coupling performance was greatly enhanced by the strategy of hot pressing than that of the traditional solid reaction method. The magnetoelectric current of BSCFAO-θ (θ = 0°) (12.06 μA/m2) was nearly 5 times higher than BSCFAO-SS (2.24 μA/m2). The magnetoelectric polarization of BSCFAO-θ (θ = 0°) (32.82 μC/m2) was nearly 4 times higher than that of BSCFAO-SS (8.31 μC/m2). The magnetoelectric coupling coefficients of BSCFAO-θ (θ = 0°) (1880 ps/m) were nearly 4 times higher than those of BSCFAO-SS (404 ps/m). The enhancement of magnetoelectric polarization of BSCFAO-θ (θ = 0°) can be attributed to the uniform c-axis orientation, which reinforced magnetoelectric polarization compared with none orientation that eliminated the magnetoelectric polarization on grain boundaries. The magnetoelectric coupling performance of BSCFAO-θ presented a gradually decreasing trend with the angle changing from 0° to 90° for the changing of orientation. Compared with traditional solid reaction methods, the strategy of hot pressing inhibits grain growth and increases grain boundaries, thus facilitating the enhancement of grain boundaries' resistivity, and the electrical resistivity of BSCFAO-θ (3.08 × 1010 Ω cm) was nearly 10 000 times higher than that of BSCFAO-SS (2.5 × 106 Ω cm), which also benefits the magnetoelectric polarization performance of BSCFAO-θ. Therefore, the hot-pressing strategy can contribute to the forming of oriented ceramics and enhance the grain boundaries' resistivity to improve magnetoelectric coupling performance. [ABSTRACT FROM AUTHOR]

Understanding of dynamical responses and mechanical characteristics of metals and alloys at high strain rates holds significant importance in fundamental physics and optimizing the performance capabilities of materials. During high-speed impact scenarios, materials may be subjected to high pressure and plastic deformation, which have the potential to modulate their mechanical attributes. In this study, high-speed planar impact experiments were conducted to investigate the progressive alterations in the microstructures and mechanical properties in coarse-grain body-centered cubic (bcc) iron subjected to high-strain-rate (approximately 2.60–3.89 × 106 s−1) impact reaching approximately 15 GPa in a one-stage light-gas gun. The nanoindentation tests show that the nano-hardness of the post-shock iron improves 1.5 times from approximately 1.75–2.70 GPa. Microscopic analyses of the post-shock bcc-iron show no significant grain refinement but a noticeable increase in the twin boundaries (TBs) and low angle grain boundaries (LAGBs) proportion with increasing shock pressure. Therefore, the interaction between TBs, LAGBs, and dislocations in post-shock iron grains plays an important role in mediating its mechanical properties. Our findings serve as possible guidance for exploring the mechanical properties of single-crystalline and poly-crystalline iron-based materials, such as steel, with optimized mechanical performance. [ABSTRACT FROM AUTHOR]

Two-dimensional colloidal crystals assembled from polystyrene nanospheres have emerged as a pivotal foundation for fabricating large-area nano-functional surfaces. These assemblies, defined by their hexagonal close-packed configuration and interlaced with grain boundaries, have garnered significant attention for applications in plasmonic structures, catalysts, photonic crystals, and inverse opals. Nonetheless, achieving consistent large-scale regularity has proven challenging due to unpredictable crystal growth and the introduction of defects. Utilizing acoustic waves excited from the airside, our experiments demonstrate the significant effects of such waves on the self-assembly process, leading to larger crystal domains and reduced defects. In comparison to the extensively studied water-end excitation techniques, our air-end excitation method introduces a novel dynamic in regulating colloidal monolayer crystallization and presents a comprehensive analysis of varying acoustic parameters, frequency, amplitude, and waveform. These findings reveal the potential of airside acoustic annealing in refining the structure of two-dimensional colloidal arrays. To elucidate our experimental observations, we delve into the theoretical underpinnings of particle dynamics, driven by classical hydromechanical constraints like surface tension and gravity. Using a qualitative estimate, we shed light on the resonant excitations and their potential role in optimizing the self-assembly process, especially focusing on resonances pertinent for enhancing cluster enlargements. Conclusively, our research, steeped in robust theoretical frameworks and groundbreaking experimental techniques, offers a multifaceted solution for perfecting two-dimensional colloidal arrays. This combined approach not only broadens the scope of acoustically induced crystallization but also charts a path for its adoption across diverse environments, signaling transformative prospects for nanomanufacturing and optical research. [ABSTRACT FROM AUTHOR]

The structure of grain boundaries (GBs) of metals is essential in determining the solute segregation at GBs; however, its complexity prohibits the understanding of the underlying mechanism. We propose a geometric descriptor of GB segregation based on the non-local coordination number of cut surfaces from GBs, which determines the segregation energies of solutes at the grain boundaries of metals across multidimensional GB space, different solutes, and different matrices. The effectiveness of the descriptor originates from the correlation between bonding strength, d-band width, and coordination number. This descriptor only depends on the bond length and angle of pre-segregation sites at GBs and can be readily used for description and prediction. Our scheme builds a novel picture for understanding the role of GB structures in segregation and provides a useful tool for the design of advanced alloys. [ABSTRACT FROM AUTHOR]

Due to fascinating physical properties powered by remarkable progress in chemical vapor deposition of high-quality epilayers, diamond thin films attract great attention for fabrication of nitrogen-vacancy-based solid-state spin systems capable of operating in ambient conditions. To date, diamond heteroepitaxy via bias-enhanced nucleation is an unavoidable method for reliable wafer-scale film manufacturing. In this work, we analyze the coalescence phenomena in nitrogen doped, heteroepitaxial diamond epilayers, with a particular focus on their specific role in the annihilation of macroscopic crystal irregularities such as grain boundaries, non-oriented grains, and twinned segments. Here, we also report on the growth mechanism for the "primary" crystal orientation along with a predominant formation of two different types of boundaries highlighting the {011}-type as a main source of the crystal lattice irregularities. [ABSTRACT FROM AUTHOR]

This study explores the feasibility of precisely tuning the resistive switching behavior of Au/BiFeO 3 /Pt/Ti/SiO 2 /Si memristors through controlled modulation of laser energy density during pulsed laser deposition (PLD). By systematically reducing the laser energy density within the fabrication process, notable alterations in the properties of the BiFeO 3 (BFO) thin film are observed. As the laser energy density decreases, the grain size in the BFO film and the thickness of the film decrease. Furthermore, we obtain the minute structural variations in response to the diverse laser energy densities employed during the deposition process. Energy-dispersive x-ray spectroscopy analysis is employed to investigate the distribution of Ti 4 + ions within the BFO thin film. The reduction in the grain size and film thickness, along with the prominent nucleation of specifically oriented grains, and the diffusion of Ti 4 + ions, lead to the BFO memristor fabricated with a lower laser energy density having more grain boundaries and a shortened conduction path (grain boundary) in the thickness direction. Consequently, the enhanced movement of oxygen vacancies facilitates their preferential accumulation along the grain boundaries within the BFO layer, resulting in an augmented on/off ratio, rectification factor, and set current in the devices. Overall, our findings explain the significant influence of laser energy density in PLD on the microstructure and electrical properties of BFO thin films. Particularly, the lower energy densities are employed to improve electrical characteristics. This research not only enhances our fundamental understanding but also provides valuable insights into optimizing BFO memristors for reliable, robust, and practical applications. [ABSTRACT FROM AUTHOR]

Fast carrier dynamics in organic thin-film transistors (OTFTs) was investigated by time-resolved electrostatic force microscopy (tr-EFM). We found that the carrier diffusion in the OTFTs proceeded in two stages: fast diffusion and slow diffusion. By applying the instantaneous frequency method to EFM, the temporal evolution of the spatial distribution of fast carriers in the channel region of the OTFTs, which took place on the timescale of several hundreds of nanoseconds, was evaluated. The inhomogeneous distribution of the local decay time constant showed that the carrier diffusion of the OTFTs was limited by the grain boundaries between each crystalline region. The quantitative capability of the method was verified by comparing the values of the carrier mobility estimated by the tr-EFM measurement and a numerical simulation. The mobility estimated from the experiment and the simulation showed good agreement, showing the possibility of the tr-EFM to evaluate the time evolution of dynamic phenomena in semiconductor devices. [ABSTRACT FROM AUTHOR]

In this work, the distribution and segregation behaviors of helium (He) and the effect of yttrium (Y) on these behaviors in the symmetrical tilt tungsten (W) Σ5(310)/[001] grain boundary (GB) region were studied using first-principles calculations. The results revealed that the GB has a significant impact on the behaviors of He in W. The solution and segregation energies of He in the W Σ5(310)/[001] GB region increase with increasing the distance from He to the GB and are inversely proportional to the effective electrons of He. The density of states analysis showed that the GB can suppress partial hybridization between He and W atoms. In addition, we find that the strengthening element Y facilitates the dissolution of He in the W GB region. [ABSTRACT FROM AUTHOR]

Highly degenerate n-type CdO with high electron mobility is a promising transparent conducting oxide (TCO) for optoelectronic devices utilizing a spectrum in the Vis-NIR range. In particular, it has been shown that doped CdO thin films can show much superior transparency of >80% in the NIR region compared to conventional transparent conducting oxide (e.g., Sn-doped In2O3) thin films with a similar sheet resistance. However, CdO thin films typically experience rapid degradation in their electron mobilities when exposed to environmental conditions with H2O moisture. Here, we studied the effects of thermal annealing on the environmental stability of In-doped CdO (CdO:In) using a combination of different analytical techniques. CdO:In thin films with different In concentration (0%–8.3%) synthesized by magnetron sputtering were subjected to different post-thermal annealing (PTA) and then aged in different environmental conditions with varying relative humidity (RH) in the range of 0%–85%. Our results reveal that the degradation of CdO:In thin films can be primarily attributed to the oxygen vacancy-related defects at the grain boundaries, which can readily react with the OH− in the moisture. The moisture induced degradation can be mitigated by appropriate PTA at high temperatures (>400 °C) where grain boundary defects, primarily associated with Cd vacancies, can be passivated through hydrogen (H), thus enhancing their environmental stability. The present study provides a comprehensive understanding of the instability mechanisms and defect passivation in transparent conducting CdO:In thin films, which can also be relevant for other wide gap oxides. [ABSTRACT FROM AUTHOR]

Understanding the mechanical behavior of nanotwinned materials in alloys is essential, particularly in relation to solute-influenced twin boundary (TB) migration. This research employs atomistic simulations and theoretical analysis to explore the influence of solute atoms on TB migration in CuAg alloys. Contrary to conventional beliefs, simulations reveal that solute Ag atoms enhance TB migration, challenging established perceptions. Nudged elastic band calculations confirm that Ag solutes substantially reduce energy barriers, shedding light on the mechanism driving solute-enhanced TB migration. This work opens novel avenues for investigating point defect impacts on TB mobility, offering insights into alloy element roles in grain boundary migration and polycrystalline material properties. [ABSTRACT FROM AUTHOR]

Amorphous intergranular films (AIFs) have been proven in experiments to improve the damage tolerance of nanocrystalline materials. However, a quantitative study is still lacking. Molecular dynamics simulations were performed here to investigate the effect of CuNb AIFs on the fracture toughness of nanocrystalline Nb. In order to clarify the role of AIFs, a bicrystal Nb model with one straight symmetrical tilt grain boundary and a mode-I crack in one of the grains was constructed, in which the AIF effect was introduced by replacing the normal grain boundary with a CuNb AIF. Then, AIF thickness-dependent tensile deformation of the bicrystal Nb samples was simulated. The work-of-fracture, which is defined as the released strain energy due to the newly generated unit area in the crack during stretching, was employed to quantify the fracture toughness of the bicrystal systems. The results show that the fracture toughness of the AIF sample can be tripled due to the blunted crack tip and the relieved stress concentration at the crack tip as compared to the AIF-free one that exhibits a brittle crack propagation behavior. Also, the thicker the AIFs, the more pronounced this reinforcing effect. More importantly, it is found that there exists a critical AIF width of 1.7 nm, below which the crack will eventually break through the AIF, and above which the crack failed to do this. It is revealed that the enhanced fracture toughness originated from the transformation of brittle crack propagation to abundant dislocation emission from AIFs. [ABSTRACT FROM AUTHOR]

Body-centered-cubic–face-centered-cubic (bcc–fcc) multi-metallic nanoparticles (NPs) associating a single-crystal core (Fe, FeCo alloys, etc.) with a polycrystalline noble metal shell (Au, AuAg alloys, etc.) are perfectly symmetrical or more irregular, even dramatically dissymmetrical, yet presenting a good crystalline organization. Here, a combination of experimental analysis and theoretical symmetry analysis is proposed, in order to provide a unified description of the observed morphologies (Fe–Au and Fe–AuAg systems), whatever their symmetry, and predict some morphology variability in a population of NPs. First, the central role of the crystal lattice accommodation is comprehensively analyzed from the experimental Fe–AuAg system. The two possible bcc–fcc epitaxial relationships generate a core–shell interface in the shape of a truncated rhombic dodecahedron. This results in two different types of grains in the shell, which are elastically accommodated between them by an equal distribution of twins and low-angle grain boundaries, however, at the cost of internal stresses. At the same time, symmetry breaking results from two possible growth variants originating from the Nishiyama–Wasserman epitaxial relationships. The shell grains fit together in a nanopuzzle-like organization, resulting in a large number of possible arrangements distributed in 13 different point groups of symmetry, all of lower order than the core symmetry (highest order of cubic symmetry). If the variants are randomly distributed, the probability for the NP to be asymmetric (group 1) is 80%. The dissymmetrical development of the NPs is then discussed. Extending this approach to other core shapes succeeds in predicting dissymmetrical or dramatically off-centered morphologies experimentally observed in Fe–Au NPs. [ABSTRACT FROM AUTHOR]

The solid-state synthesized dense ceramic composite, consisting of M-type hexaferrite Ba 0.5 Sr 0.5 Fe 12 O 19 and inverse spinel ferrite Ni 0.3 Co 0.2 Zn 0.5 Fe 2 O 4 (NCZFO) with varying concentrations, demonstrates the presence of apparent colossal permittivity along with dielectric relaxation behaviors at the higher frequency regions for all the composites. This phenomenon manifests as a giant dielectric permittivity of approximately 10 5 at 1 kHz, gradually decreasing to around 10 3 at 1 MHz at room temperature. It can be attributed to the Maxwell–Wagner interfacial polarization, which arises from the presence of different conductivity regions within the microstructures of the composite. The dielectric permittivity and the activation energy are also increased with higher NCZFO content, indicating an intricate microstructure influencing the electrical response by impacting charge carrier movement and ion migration. The presence of both Fe and Co cation defects and oxygen vacancies enhanced non-uniformity in the microstructure with different conductivity regions. The appearance of relaxation peaks in the higher frequency region can be attributed to inhomogeneity in the microstructure. In conjunction with the equivalent circuit analysis, the Nyquist plot confirmed that the electrical response at a lower frequency primarily arises from grain boundaries. The departure from ideal Debye-type relaxation behavior in the electrical response is also confirmed by impedance analysis. Furthermore, the step-like increase in AC conductivity with frequency suggests that the electrical response observed at a lower frequency is not intrinsic. Rather, it indicates the depletion of insulating grain boundaries due to diffusive ion motions resulting from defects. This observation reinforces that the high dielectric permittivity observed in the composite is not an inherent characteristic of the constituent materials. Instead, it arises from the microstructure and the influence of defects within the material. [ABSTRACT FROM AUTHOR]

Grain rotation caused by the movement of dislocations is a determinant factor for the mechanical behavior of metals. In general, the grain rotation may be mediated by grain boundary dislocations (GB-dis) and intragranular dislocations (In-dis), which are closely associated with grain size. Few works have investigated how grain size depends on grain rotation, and the competitive mechanism between GB-dis and In-dis remains unclear. The present work investigates the structural evolution and deformation of coarse-grained tungsten under high pressure. The results show that under high pressure, the nano-sized grains preferentially rotate with dislocation climbing in GBs. Under high pressure, In-dis migrate faster across coarse grains and are absorbed by GBs on the other side, resulting in grain rotation. Elevated temperature also facilitates the migration of In-dis to arrive GBs where they can be absorbed by GBs, thus promoting grain rotation. The theoretical results show that grain rotation occurs easily under high pressure and high temperature. With increasing grain size, the stress-induced rotation mechanism goes from being dominated by GB-dis to being dominated by In-dis migration. The competitive relationship between GB-dis and In-dis during grain rotation is elaborated, providing a new strategy for designing materials under high pressure. [ABSTRACT FROM AUTHOR]

The thermal conductivity (k) of polycrystalline SiC thin films is relevant for thermal management in emerging SiC applications like microelectromechanical and optoelectronic devices. In such films, k can be substantially reduced by microstructure features including grain boundaries, thin film surfaces, and porosity, although these microstructural effects can also be manipulated through thermal annealing. Here, we investigate these effects by using microfabricated suspended devices to measure the thermal conductivities of nine low-pressure chemical vapor deposition SiC films of varying thicknesses (from 120 to 300 nm) and annealing conditions (as-grown and annealed at 950 and 1100 °C for 2 h, and in one case 17 h). Fourier-transform infrared spectroscopy, x-ray diffraction spectra, and density measurements are also used to characterize the effects of annealing on the microstructure of selected samples. Compared to as-deposited films, annealing at 1100 °C typically increases the estimated grain size from 5.5 to 6.6 nm while decreasing the porosity from around 6.5% to practically fully dense. This corresponds to a 34% increase in the measured thin film thermal conductivity near room temperature from 5.8 to 7.8 W/m K. These thermal conductivity measurements show good agreement of better than 3% with fits using a simple theoretical model based on the kinetic theory combined with a Maxwell–Garnett porosity correction. Grain boundary scattering plays the dominant role in reducing the thermal conductivity of these films compared to bulk single-crystal values, while both grain size increase and porosity decrease play important roles in the partial k recovery of the films upon annealing. This work demonstrates the effects of modifying the microstructure and, thus, the thermal conductivity of SiC thin films by thermal annealing. [ABSTRACT FROM AUTHOR]

Despite extensive studies of spin transport in metallic structures, it remains a challenge to achieve spin relaxation length well above 1 μm in metals even at low temperatures. We explore nonlocal spin transport in Cu channels with a cross section of 0.5 × 0.5 μm2, which exhibit superior values of electrical conductivity and residual resistivity ratio (RRR). Based on structures fabricated in a single batch, we found an average spin relaxation length of λ C u = 3.2 ± 0.7 μ m and an average spin relaxation time of τs = 120 ± 50 ps at 30 K. Substantial variations of λ C u , RRR, and resistivity ρ C u are found among the structures and the three quantities correlate well to one another. The most conductive Cu channel in the batch yields λ C u = 5.3 ± 0.8 μ m and τ s = 250 ± 80 ps. These superior values exceed expectations for metals and can be attributed to reduced spin relaxation from grain boundaries and surfaces. [ABSTRACT FROM AUTHOR]

The stability of holes in solid thin films is crucial, as an absence of holes is necessary in some applications and holes are needed in others. We develop an axisymmetric two grain model with a central hole, with surface diffusion governing the exterior surfaces and mean curvature motion governing the grain boundary. The model can exhibit grooving, wetting, dewetting, as well as void, hole, and hillock formation. Here, we extend an earlier work [Zigelman and Novick-Cohen, J. Appl. Phys. 130, 175301 (2021)], where it was shown for an axisymmetric single grain system with a hole at the center that there exists a critical effective radius, which is independent of the contact angle. The stability of the steady states, which consist of coupled nodoidal and catenoidal surfaces, is analyzed numerically by imposing the steady state configurations as initial conditions. This approach yields stability criteria in terms of (i) the effective energy, (ii) the ratio between the maximal thickness of the inner and outer grains, (iii) a generalized effective radius, and (iv) the ratio between the mean curvature of the exterior surfaces and the total volume of the system. Some of these criteria partially reflect the Rayleigh stability criterion. Hillock formation tends to be stabilizing. Modes of instability include growth of one grain at the expense of the other, breakup induced by grooving, and hole closure. [ABSTRACT FROM AUTHOR]

Rare-earth nickelates (RENiO3: RE≠La) exhibit metal–insulator transition (MIT) properties that enable potential applications, such as critical temperature resistance thermistors, optoelectronic switches, and correlated logical devices. Nevertheless, their abrupt structural distortion across MIT results in mechanical stresses and forms microcracks within the bulk RENiO3, and this irreversibly reduces their resistive change during MIT that further impedes their practical applications. Herein, we demonstrate a compositing strategy that simultaneously improves the MIT performances and mechanical strength of RENiO3 by introducing a secondary phase of perovskite oxides with similar lattice parameters and high resistivity. Despite its much higher resistivity compared to RENiO3 (e.g., RE = Sm or Pr), introducing the LaMnO3 compositing phase under high oxygen pressure surprisingly reduces the matrix resistivity. Furthermore, such a compositing process (e.g., 20% LaMnO3) also effectively improves the mechanical strength of RENiO3 by eight times. Such counterintuitive variations are attributed to the similar structure and lattice parameter between RENiO3 and the perovskite composites that modify the grain boundary. As a result, the resistive change is more abrupt across MIT owing to the reduction in the resistivity associated with the grain boundary, while the defect generation and propagation are also suppressed that improves the mechanical properties. This further pave the way to the application of bulk RENiO3 as discrete devices in correlated electronics. [ABSTRACT FROM AUTHOR]

Inferior morphology of perovskite films and suppressed hole extraction restricts the performance of perovskite solar cells (PSCs) with a PEDOT:PSS hole transporting layer (HTL). In this work, poly-TPD is used to modify the surface of PEDOT:PSS films in PSC. The presence of hydrophobic poly-TPD decreases the nucleation sites, and as a result, perovskite films with larger grains are obtained. Improved energy level alignment in the presence of poly-TPD results in enhanced hole extraction from the perovskite layer to the HTL. The improved morphology and charge extraction resulted in improved photovoltaic performance. The power conversion efficiency (PCE) of PSCs was increased from 13.6% to 16.1% with the incorporation of poly-TPD. Also, the shelf life of the PSCs has exhibited considerable improvement due to the presence of hydrophobic poly-TPD and fewer number of grain boundaries. After 66 days, the PSC with poly-TPD maintained 96% of its initial PCE, whereas the PCE of the control device degraded to 72% of its initial value. [ABSTRACT FROM AUTHOR]

This study investigates the structural stability of the CeO2-ZrO2 system when subjected to high doses of irradiation (a few hundred displacements per atom). The goal is to explore their potential use in safe immobilization of spent nuclear fuel and development of accident-tolerant fuels for next-generation nuclear reactors. Highly dense pellets were synthesized using a solid-state reaction and then irradiated with 1.75 MeV Xe5+ ions at ion fluences ranging from 1 × 1015 to 1 × 1017 ions/cm2. Structural and microstructural analyses were conducted using glancing angle x-ray diffraction, micro-Raman spectroscopy, and scanning electron microscopy. The results indicate that Ce0.8Zr0.2O2 has a high tolerance against irradiation-induced phase transformation or amorphization but does generate irradiation-induced point defects. Each energetic ion produced a deformed region with a voluminous swelling of ∼0.61 ± 0.09 nm and a damaged zone of ∼0.09 ± 0.02 nm, as calculated from the irradiation-caused peak broadening that is explained by a three-step damage accumulation model. The electron microscopy studies show that grain boundaries serve as a sink for defects, and an increase in grain size was observed due to defect accumulation inside the grain's volume. Overall, the study shows that polycrystalline fluorite-structured Ce0.8Zr0.2O2 is a promising nuclear material for advanced energy systems as it did not show significant structural damage such as amorphization and grain fragmentation, even on irradiation at a high dose of ∼428 dpa. [ABSTRACT FROM AUTHOR]

Polycrystalline thin films are widely used for devices and energy-related applications, such as power electronics, solar cells, and thermal management of devices. In many cases, large-scale crystallization during thin-film growth is challenging, so columnar grains are often found in metal and semiconductor thin films. These rough columnar grain boundaries may also have different phonon specularities from that for typically smoother top/bottom film surfaces. A simple analytical model to separately treat these boundaries and interfaces for phonon scattering is currently unavailable, although the in-plane thermal transport is critical to heat spreading within thin-film devices. In this paper, we extend the effective medium formulation from three-dimensional polycrystalline bulk materials to columnar-grained thin films. The model predictions agree well with those given by frequency-dependent phonon Monte Carlo simulations, considering varied phonon specularity at top/bottom film surfaces and grain-boundary phonon transmissivity. The analytical model is further used to analyze the existing data on polycrystalline ZnO thin films with columnar grains. [ABSTRACT FROM AUTHOR]

In this paper, we report the use of three pendeo-epitaxy growth approaches as a way of reducing the threading dislocation density (TDD) of 20 × 20 μm2 GaN platelets to be used for the development of micro light-emitting diodes (μLEDs). The method relies on the coalescence of GaN crystallites grown on top of a network of deformable pillars etched into a silicon-on-insulator substrate. Our approach takes advantage of the creeping properties of SiO2 at the usual GaN epitaxial growth temperature, allowing the GaN crystallites to align and reduce the grain boundary dislocations. Furthermore, this bottom-up approach allows to get rid of the dry plasma etching step for μLEDs fabrication, which highly deteriorates sidewalls, reducing the efficiency of future displays. By optimizing the growth conditions and inducing asymmetric nucleation, a TDD of 2.5 × 108 cm−2 has been achieved on the GaN platelets, while keeping a smooth surface. [ABSTRACT FROM AUTHOR]

Lithium ions shuttle between electrodes through the ceramic solid electrolyte across the boundary regions in a solid-state Li-ion battery. This work demonstrates how phonon vibrations get altered by sintering conditions, and grain boundaries (GBs) could be useful in enhancing the ionic conductivity of solid electrolytes. GB engineered Li1.3Al0.3Ti1.7(PO4)3 (LATP) ceramics are prepared using a sol-gel process and performed sintering under different conditions, viz., spark plasma sintering (SPS) and conventional isothermal sintering (CIS). The former exhibits GB regions with amorphous characteristics, whereas the latter shows a sharp boundary between crystalline grains. LATP-SPS ceramic shows two orders of higher ionic conductivity (σ = 1.02 × 10−5 S/cm at 300 K and 100 Hz) than LATP-CIS. We investigate the interrelation between lattice vibration and lithium-ion migration by monitoring the changes in vibrational mode characteristics of LATP ceramics through temperature-dependent Raman spectroscopy. Raman modes of LATP-SPS exhibit a higher Raman shift (∼2 cm−1 at 123 K) due to increased defects, preferentially from grain boundary regions, compared to the LATP-CIS pellet. Most of the vibrational modes undergo a red shift (∼10 cm−1) with increasing temperature, except for the O–P–O bending mode [A1g(3)], which exhibits a blue shift (∼3 cm−1). These observations correlate with interstitial ionic migration in the LATP framework. Force constant of the observed Raman modes suggests that lithium-ion migration is assisted significantly by dynamic structural changes of the (PO4)3− sublattice. Anharmonicities observed from temperature-dependent changes in Raman profiles are explained using three-phonon and four-phonon scattering processes, which lower the migration barrier and, hence, contribute to higher ionic conductivity. [ABSTRACT FROM AUTHOR]

The metal–insulator transition (MIT) in polycrystalline vanadium dioxide (VO2) is less sharp than in single-crystal VO2 due to the presence of grain boundaries (GBs). The MIT causes a resistivity change (Ron/Roff) across the MIT to decline from the single-crystal value of ∼104 and also causes a larger hysteresis across the transition. The properties of GBs in VO2 are studied as a function of GB tilt angle. We find that V–V site pairing, which causes a monoclinic phase VO2 to be semiconducting in bulk, also controls bandgap opening at GBs, thus influencing the overall metal–insulator behavior. The almost linear relationship between the ratio of adhesion energy divided by two times the surface energy and the GB energy indicates that the GB energy of twin GBs is primarily determined by re-binding across the GB rather than by the corresponding surface energy. Moreover, a steeper linear fit, characterized by a slope of 0.62, observed in the monoclinic phase VO2 suggests that the GB energy and stability have a higher tolerance to interfacial distortion at the boundary, compared to the rutile phase VO2 and TiO2. [ABSTRACT FROM AUTHOR]

Nb is considered a promising candidate as a refractory element due to its high-temperature endurance, excellent thermal conductivity, and compatibility with liquid-metallic coolants in nuclear reactors. In the present study, radiation-based molecular dynamics numerical simulations were conducted in Σ 13, Σ 29, and Σ 85 symmetric tilt grain boundary models for pure Nb specimens. The stochastic high-energy collisions were modeled via large-scale atomic/molecular parallel simulator code to accurately investigate the radiation-induced defects generated in the order of picoseconds at the atomic level. The long-range embedded atom method potential and coulombic repulsive Ziegler–Biersack–Littmark potentials were smoothly overlaid for precise force-field interactions among Nb atoms. To investigate the ability to arrest the radiation-induced damage, the bi-crystal Nb specimens were irradiated at varying magnitudes of primary-knock-on atom (PKA) energies EPKA = 10 20, and 30 keV at temperature regimes 300, 600, and 900 K, respectively. The Frenkel pairs, complex linear defects, distribution of point defects as clusters, rate of defect annihilation, and temperature fluctuations within the displacement cascades of irradiated Nb specimens were comprehensively studied and reported. Here, the Nb-Σ 29 GB model survived with the lowest number of residual defects. Also, the recombination rate of the irradiated Nb specimens increases with the increase in temperature and PKA energy magnitude due to enhanced atomic mobility of the dislodged atoms. Hence, the bi-crystal Nb specimen can be favored for a radiation-tolerant material as structural components in next-generation reactors. [ABSTRACT FROM AUTHOR]

In this work, the conduction mechanism in B a x S r 2 − x CrMo O 6 (0 ≤ x ≤ 0.3) double perovskite has been investigated using different techniques, such as universal dynamic response (UDR) and modulus spectroscopy. AC impedance spectroscopy has been studied in the frequency range of 0.3 Hz–5 MHz in a wide range of temperatures. It has been found that the conduction mechanism is thermally activated and frequency-dependent. The impedance fitting response to the microstructure reveals that grain boundaries are more resistive and capacitive than grains. Analysis of the complex modulus indicates that both short- and long-range charge carrier transport is responsible for conduction with non-Debye-type response in these oxides. The permittivity analysis indicates the existence of both universalities, near constant loss and UDR. Furthermore, from the Almond West power law, hopping frequency (ω c) and activation energy E a c have been calculated. The relaxation time and DC conductivity are found to obey Barton Nakajima and Namikawa's relation. In addition, the Kramers–Kronig relation and conductivity scaling are discussed to validate the impedance data and provide insight into the conduction processes in this mixed ionic electronic conductor. [ABSTRACT FROM AUTHOR]

High-entropy alloys exhibit great potential for cryogenic applications. This study investigates the nano-scratching behavior of CuCoCrFeNi high-entropy alloy at a cryogenic temperature (77 K) using molecular dynamics. Results show that compared with the single-grain model, the average friction coefficient (AFC) increases for all three polycrystalline models with different grain sizes d, but the anti-wear property can be improved by 28.5%, when grain size d = 10.7 nm. The smaller friction on the scratching surface of the single-grain model (AFC is 15.5% less than that of the model with d = 8.2 nm), which makes the overall temperature rise lower compared to that of the polycrystalline models. However, due to the stress concentration released when a complete stacking fault tetrahedron is produced, the single-grain model cannot significantly harden the surface and subsurface to a greater degree. In the polycrystalline models, dislocations are blocked at grain boundaries (GBs). However, the introduction of GBs changes the von Mises stress distribution. Finally, an attempt was made to reveal the role of yield pressure H3/E2 (H—hardness, E—elastic modulus) in friction-reducing and anti-wear properties. [ABSTRACT FROM AUTHOR]

Using first-principles density functional calculations, we investigate the structure and properties of previously unstudied grain boundaries (GBs) in the solar absorber material copper-zinc-tin-sulfide (CZTS). We identify four stable low-Σ value symmetric tilt GBs with low formation energies: Σ3 (111) and Σ5 (201), each with two different GB terminations. Compared to CdTe and CuInSe, GBs in the quaternary semiconductor CZTS exhibit a wider variety of electronic states due to the more complex chemical environment near the GB, including under-coordinated atoms and dangling bonds. Further analysis confirms that strong dangling bonds introduce deep gap states in all GBs studied. We also investigate segregation and electronic properties of intrinsic point defects to GBs and find that one of the Σ3 (111) GBs exhibits an abnormal defect segregation behavior that favors Cu-poor (Zn-rich) GB composition, which is beneficial for its overall performance. [ABSTRACT FROM AUTHOR]

The content of free oxygen O ad at the ZnO grain boundaries has an important impact on the double Schottky barrier and electrical properties of ZnO varistors. In this work, Bi–Er–O pre-synthesized (BE) phase (Bi 1- x Er x) 2 O 3 (0.25 < x < 0.455) with high conductivity of O ad was prepared using Bi 2 O 3 and Er 2 O 3 as raw materials, and the effects of the BE phase doping on the phase, grain boundary properties, and electrical properties of ZnO–Bi 2 O 3 –Sb 2 O 3 –Co 2 O 3 –MnO 2 –Cr 2 O 3 –SiO 2 varistors were studied. XRD analysis shows that the lattice constant of the BE phase (Bi 1- x Er x) 2 O 3 is between (Bi 0.75 Er 0.25) 2 O 3 and BiErO 3. With increasing doping content of the BE phase from 0 to 0.75 wt%, part of Er3+ still exists in the form of the BE phase (Bi 1- x Er x) 2 O 3 at the ZnO grain boundaries, and its content increases with increasing doping content of the BE phase. The conductivity of O ad in (Bi 1- x Er x) 2 O 3 is much higher than that in Bi 2 O 3 , resulting in the generation of a large number of negative O′ and O″ at the ZnO grain boundaries, and decreasing concentration of the intrinsic point defect zinc interstice Zn i. So the donor concentration N d decreases, the height of the grain boundary barrier increases, the depletion layer widens, and the electrical properties are improved. By analyzing the low-temperature permittivity spectra, it was calculated that with increasing doping content of the BE phase from 0 to 0.75 wt%, the concentration of oxygen vacancy V O • decreases inappreciably, but the concentration of zinc interstice Zn i • • decreases by about 23%. When the doping amount of the BE phase is 0.75 wt%, the nonlinear coefficient α of the obtained ZnO varistors is 73.9 ± 0.6, and the leakage current density J L is only 0.3 ± 0.1 μA/cm2. This study provides an important reference for improving the electrical properties of ZnO varistors by manipulating the Bi-rich phase structure to improve the double Schottky barrier characteristics. [ABSTRACT FROM AUTHOR]

The effects of varying γ′ size and grain boundary carbide distribution at elevated temperatures on the fatigue behavior of turbine disk alloy RR1000 were examined through combining 2D and 3D imaging characterization. The fatigue crack growth rate at 725°C is higher than at 650°C due to enhanced oxidation damage at higher temperature, dominated by an intergranular fracture mode. This is more marked with longer dwell time (linked to diffusion time) and when carbides have formed continuously at grain boundaries. The fatigue crack path was characterized by X‐ray CT scan to present the complex 3D crack propagation morphology. It is noted that a discontinuous crack path and uncracked ligaments can be discerned ahead of the crack tip particularly in the microstructure where carbides are continuously formed at grain boundaries. This is linked to embrittled zones ahead of the crack tip formed during longer dwell times at the maximum stress during cycling at elevated temperature. Highlights: Effects of microstructure and temperature on fatigue crack growth of Ni‐based superalloy.Deeper understanding of high‐temperature fatigue mechanism by 2D/3D image characterization.X‐ray CT scan revealing complex 3D crack morphology linked to oxidation fatigue mechanism. [ABSTRACT FROM AUTHOR]

Liquid phase sintering aids play an important role in facilitating grain growth and promoting texture formation. However, these sintering aids remain at grain boundaries after sintering, leading to a deterioration in the properties and hindering the reproducibility of textured ceramics. In this study, we employed the templated grain growth (TGG) method to synthesize [001]-textured Pb(Mg 1/3 Nb 2/3)O 3 –PbZrO 3 –PbTiO 3 (PMN-PZT) piezoelectric ceramics, and implemented a crucial post-annealing step to remove the residual PbO. The effect of annealing temperatures on the microstructure, dielectric and piezoelectric properties of the textured ceramics was investigated. The results demonstrate the substantial influence of annealing temperature on these properties. Specifically, annealing at 800 °C led to a significant enhancement, with the ε r at room temperature increasing from 2277 to 2410, and the k 33 improving from 0.85 to 0.88. Consequently, the d 33 increases from 1080 to 1220 pC/N. This study emphasizes the effectiveness of the post-annealing treatment in improving the properties and reproducibility of textured piezoelectric ceramics, which is particularly crucial for the mass production of textured ceramics. [ABSTRACT FROM AUTHOR]

According to the literature reports, synthesis of Ba 1- x Ca x TiO 3 (BCT) ceramics with good microstructure and satisfactory dielectric property is still a challenge. So, a facile tartaric coprecipitation method in the study is proposed to prepare BCT fine powders with homogeneous morphology, high crystallinity and tetragonality. The effect of Ca2+ doped concentration on microstructure and dielectric property was studied. Results showed that, the characteristics of the raw BCT powders greatly affected the microstructure and site occupancy of Ca2+ in BT ceramics, which subsequently played a crucial rule on the dielectric performance. Owing to the good properties of the raw BCT powders, the as-obtained ceramics demonstrated good microstructure with uniform grain size of ∼1 μm, defined grain boundaries and densely packed without any cracks or pores. In addition, they also demonstrated much improved dielectric properties with good ε r , low tan δ , definite increase of Tc , suggesting they are compatible in application of MLCC with high performance. [ABSTRACT FROM AUTHOR]

Transparent hexagonal 2 at.% Yb:Sr 5 (PO 4) 3 F (S -FAP) ceramics were effectively fabricated by hot pressing the coprecipitated powder employing LiF as the sintering additive. The effects of LiF doping levels (0–0.5 wt%) and sintering temperature (820–940 °C) on microstructural development and optical characteristics of samples were examined. The results showed that the addition of LiF and the evaluated sintering temperature accelerated the grain development and densification process of Yb:S-FAP ceramics. Also, the full densification process of low-doped LiF ceramic samples was found to be strongly dependent on the reduced sintering temperature. For the Yb:S-FAP transparent ceramic sintered at the lowest temperature of 850 °C than previously reported with 0.1 wt% LiF, which have an optical in-line transmittance of 59.7% and 79.66% at 500 and 1100 nm respectively. The corresponding scattering sources of ceramic samples were analyzed by the surface SEM of different magnification at different LiF doping concentrations, and residual LiF, residual porosity, and grain boundary scattering were considered to be the main scattering sources. The spectral results showed that the LiF-doped Yb:S-FAP transparent ceramics had a wide absorption peak at 975 nm with the full width at half maximum (FWHM) of 15 nm and possessed a fluorescence lifetime of 1.12 ms. [ABSTRACT FROM AUTHOR]

One of the primary challenges in high-power devices is the issue of heating, which is caused by energy loss resulting from domain wall motion. To address this problem, our study established a electromechanical hardening approach by integrating NiO into Na 1/2 Bi 1/2 TiO 3 (NBT). This method leads to the in-situ formation of the second phase within grains and between the grain boundaries. The second phase inside the grains inhibits the domain wall motion and reduces the mechanical loss, resulting in a considerable increase in mechanical quality factor (Q m) by over 80%. Additionally, the introduction of NiO notably enlarges the grain size by more than 4.5 times. The combination of the second phase and the increased grain size synergistically preserves piezoelectric coefficients (d 33). Our study uncovers an innovative method to enhance Q m without significantly compromising d 33. [ABSTRACT FROM AUTHOR]

The objective of this paper is to assess the impact of mineral grain size and grain size distribution of aggregates on the deterioration of pavement surface microtexture. For the study, aggregates were collected from nine different sources to cover a wide variation in mineralogical type. The grain size parameters were obtained by detecting mineral grain boundaries using scanning electron microscope electron back scattered diffraction (SEM EBSD) analysis on thin sections prepared from the aggregates. Scanning electron microscope (SEM) analysis was also carried out on thin sections of all aggregate types to determine their mineralogical composition. Microtexture deterioration was measured by collecting the British pendulum number (BPN) of the aggregate after every hour of polishing for six hours using an accelerated polishing machine. From the mineral composition analysis, it was observed that the aggregates in the study belonged to three rock types: granite, amphibolite, and basalt (three sources of each type). The BPN values of the polished stones indicated that aggregates with finer grains offer more resistance to polishing. Statistical analysis of the test results also suggests that a wide variation in grain sizes in aggregates positively contributes to resistance against polishing. The study confirmed that, for a given rock type, coarse aggregates with finer grains and greater variation in grain size can better withstand microtexture deterioration caused by mechanical polishing from vehicular loads when used in the surface course of pavements. [ABSTRACT FROM AUTHOR]

Tungsten carbide was manufactured by picosecond laser in this study. Shapes of the ablated craters evolved from parabolic‐like (less than 10 pulses) to Gaussian‐like (more than 500 pulses) as the pulse number increased. The shape changes were closely associated with the discontinuous diameter expansion of ablated crater. To explain these phenomena, two thresholds were identified: an upper threshold of 0.129 J/cm2 and a lower threshold of 0.099 J/cm2. When the laser energy exceeded the upper threshold, ablation occurred under the laser‐energy‐dominated mode. When the laser energy fell between the upper and lower thresholds, ablation occurred under the cumulative‐effect‐dominated mode. The transition of ablation mode contributed to the diameter expansion and shape change. In addition, elemental composition varied significantly at the ablated crater and heat‐affected zone (HAZ), which were related to the degrees of reactions that occurred at different distances from the laser. Finally, surface hardness decreased from base material (32.52 GPa) to edge of crater (11.59 GPa) due to the escape of unpaired interstitial C atoms from the grain boundaries. [ABSTRACT FROM AUTHOR]

In this paper, YOF was used as the sintering additive for obtaining MgAl 2 O 4 transparent ceramics with excellent optical properties. It is found that YOF enhances the densification of MgAl 2 O 4 ceramics. In addition, YOF can effectively suppress grain growth in the final stage because of the reduction of grain boundary energies and the pinning effect at the grain boundary region during the hot isostatic pressing (HIPing) process. Nevertheless, it is important to carefully control the content of YOF. Although the formation of a low amount of Y 3 Al 5 O 12 (YAG) is advantageous because its grains are doing the pinning effect at the grain boundary, an excessive amount is not desired as it is likely to cause scattering. After optimizing the YOF content and sintering temperature, the final sample (4 mm thick after polishing) with 0.01 wt% YOF HIPed at 1550 °C is obtained, showing the high in-line transmittance of 82.6% at 400 nm and high flexural strength of 271.6 MPa. [ABSTRACT FROM AUTHOR]

Controlling coordinately heterogeneous grain growth is challenging for preparing multiphase structural materials, especially for high-performance alumina-based fibers. In this study, we achieved refining the mullite grains by controlling the composition of the silicon source, resulting in the successful preparation of fine-grained alumina-mullite diphasic fibers with high thermal stability. The alumina-mullite diphasic fibers consisted of lamellar α-Al 2 O 3 and mosaic-like mullite grains with a biphasic grain size below 500 nm. The Weibull strength of diphasic fibers could reach 1.70 GPa. The strength retention rate exceeded 85% even after thermal exposure at 1100 ℃ for 50 h and at 1200 ℃ for 5 h. Moreover, our investigation revealed the presence of an ordered complexion on the (0001) plane of α-Al 2 O 3 and discussed a possible situation of its two-dimensional atomic arrangement distribution, providing great enlightenment for understanding grain boundary segregation theory. [ABSTRACT FROM AUTHOR]

Na3Zr2Si2PO12(NZSP)‐based NASICON solid‐state electrolytes (SSEs) show not only competitive ionic conductivity but also high chemical stability in air, holding a great promise for enabling the use of sodium metal anode in solid‐state sodium batteries. However, sodium (Na) metal dendrite growth inside SSE always leads to undesirable short‐circuiting in battery even no obvious changes in interfacial contact loss and interfacial decomposition during cycling. How to control Na metal dendrite growth and in situ observe the effect of SSE/Na interface change on dendrite growth is quite challenging. Herein, an in situ synchrotron‐based X‐ray imaging method is developed to systematically investigate the dendrite origin in NZSP‐based SSEs. It is find that the dendrite growth intrinsically depends on the grain boundaries (GBs) in NZSP and the NZSP/Na interfacial properties. It is confirmed that Na dendrite infiltration kinetic evolution in NZSP is strongly associated with Na ion/electron conductivity and Young's modulus of GBs. Moreover, the electro‐chemo‐mechanical phase‐field model evaluation demonstrates that the basic reason for Na metal dendrite intrusion into the GBs of SSE is a combination of local polarization potential and the presence of stress formed at GBs. [ABSTRACT FROM AUTHOR]

Developing low magnetic stainless-steel plates with high yield strength while ensuring good plasticity, corrosion resistance, and paramagnetism is a tough technical challenge, especially under conditions of limited rolling mill capacity and total reduction. In this study, a low magnetic stainless-steel plate with excellent yield strength (620 MPa), ultimate tensile strength (891 MPa), and ductility (42.7%) was prepared by rolling in the non-recrystallization region (below the recrystallization temperature Tnr) and subsequent solution treatment. The effects of different thermomechanical processing techniques on the recrystallization behavior, grain size, dislocation density, grain boundary characteristics, micro-texture, mechanical and magnetic properties of low magnetic stainless steel were studied. Compared with conventional high-temperature hot rolling, rolling in the non-recrystallization region and subsequent solid solution treatment can effectively refine the grain size and form Brass {001} < 211 > texture in the plate, with texture intensity increasing with greater deformation in this region. The main strengthening contribution mechanisms of high yield strength are N-element solid solution strengthening and fine grain strengthening. Due to the high austenite stability and appropriate rolling temperature, the paramagnetism of low magnetic stainless steel was not disrupted after rolling in the non-recrystallization region, and the relative permeability of all samples was less than 1.01. From the perspectives of production efficiency, process difficulty, and economy, the HR3-S process route in this study makes it easier to achieve large-scale industrialization, providing theoretical and process references for developing low magnetic stainless-steel plates toward high yield strength and high paramagnetic stability. [ABSTRACT FROM AUTHOR]

Single‐crystalline layered oxide (LiNi1‐x‐yMnxCoyO2) cathodes have been found to exhibit exceptional electrochemical properties when coupled with various inorganic solid electrolytes (ISEs) in all‐solid‐state batteries (ASSBs). Their advantages stem from the robust morphological integrity with the absence of grain boundaries and the high electrochemical oxidative stability. Here, ASSBs featuring single‐crystalline LiNiO2 (LNO) with the highest Ni content are reported, offering a high theoretical specific capacity of 275 mAh g‐1 alongside a high average discharge voltage (3.7 V vs Li+/Li). Through a careful investigation, it is demonstrated that micron‐sized single‐crystalline LNO (µSC‐LNO) composite cathodes with a halide ISE exhibit a high initial discharge capacity of 205 mAh g‐1 with an outstanding cycle performance over 200 cycles in room‐temperature ASSBs. The significance of engineering parameters is emphasized, such as particle size and specific density, in promoting a homogeneous and fast Li+ transport within the composite cathodes. Furthermore, the formation of undesirable interphase between the halide ISE in the cathode and sulfide ISE separator is elucidated, which may be a critical factor impeding long‐term cyclability of ASSBs. This work provides insights into the design of composite cathodes for high‐energy‐density ASSBs. [ABSTRACT FROM AUTHOR]

Aero-engines can be exposed to One Engine Inoperative (OEI) conditions during service, and the resulting overheating effect may significantly impact their structural integrity and flight safety. This paper focuses on the influence of overheating on the microstructural evolution and tensile properties of the GH4720Li alloy, a nickel-based polycrystalline superalloy commonly used in turbine disks. Based on the typical OEI operating conditions of a real aero-engine, a series of non-isothermal high-temperature tensile tests involving an OEI stage of 800 °C were conducted. The effects of OEI-induced overheating on the microstructure and tensile properties of the GH4720Li alloy were investigated. The results showed that, after OEI treatment, the primary γ′ phase in this alloy was partially dissolved. The GH4720Li superalloy also exhibited numerous microcracks at the grain boundaries, resulting in complex effects on its tensile properties. The alloy's yield strength and ultimate tensile strength were slightly decreased, whereas its ductility decreased considerably. The OEI-induced embrittlement phenomenon was mainly caused by the non-uniform distribution of the tertiary γ′ phase within grains. The formation of microcracks nucleated at the interfaces between the primary γ′ precipitates and γ matrix phase was another key factor. [ABSTRACT FROM AUTHOR]

The exceptional mechanical properties of Ni-based high entropy alloys are due to the presence of ordered L12 (γ′) precipitates embedded within a disordered matrix phase. While the strengthening contribution of the γ′ phase is generally accepted, there is no consensus on the precise contribution of the individual strengthening mechanisms to the overall strength. In addition, changes in alloy composition influence several different mechanisms, making the assessment of alloying conditions complex. Multicomponent L12-ordered single-phase alloys were systematically developed with the aid of CALPHAD thermodynamic calculations. The alloying elements Co, Cr, Ti, and Nb were chosen to complexify the Ni3Al structure. The existence of the γ′ single phase was validated by microstructure characterization and phase identification. A high-temperature compression test from 500 °C to 1000 °C revealed a positive temperature dependence of strength before reaching the peak strength in the studied alloys NiCoCrAl, NiCoCrAlTi, and NiCoCrAlNb. Ti and Nb alloying addition significantly enhanced the high-temperature yield strengths before the peak temperature. The yield strength was modeled by summing the individual effects of solid solution strengthening, grain boundary strengthening, order strengthening, and cross-slip-induced strengthening. Cross-slip-induced strengthening was shown to be the key contributor to the high-temperature strength enhancement. [ABSTRACT FROM AUTHOR]

Iron-enriched ferroelectrics are of particular interest as piezoactive components of piezoelectric-ferrite ME ceramics. This is due to the phase composition similarity and the reduction of expected interfacial doping effects during high-temperature calcination. This idea seems attractive, but laborious due to the significantly limited number of possible piezoelectric–ferrite combinations. Therefore, there is practically no data on such systems in the literature. ME composite ceramics based on the highly efficient Fe-containing Pb(Fe 0.5 Nb 0.5) 0.935 Ti 0.065 O 3 (PFNPT) ferroelectric has been studied. (100-х) wt.% Pb(Fe 0.5 Nb 0.5) 0.935 Ti 0.065 O 3 (PFNPT) + х wt.% Ni 0.9 Co 0.1 Cu 0.1 Fe 1.9 O 4-d (NCCF) composite systems has been obtained by the solid-state method at 1050 °C, with no foreign phases. The specimens densities amounted to ∼80% of the theoretical. It has been shown that the ME conversion efficiency and other composites properties are significantly influenced by the PFNPT precursor pre-treatment method. The maximum value of the ME coefficient ΔΕ/ΔΗ = 75 mV/(cm Oe) has been observed for specimens with x = 50–60 made from PFNPT powder with the addition of Li 2 CO 3. An increase in the ME composites sintering temperature to 1150 °C leads to the formation of Pb 2 Nb 2 O 7 foreign phase with a pyrochlore structure along the grain boundaries. The ME coefficient ΔΕ/ΔΗ does not exceed 15 mV/(cm⋅Oe). There is an threefold decrease in the composites piezoelectric parameters (piezoelectric coefficients d ij , g ij), as well as in their magnetic properties (magnetizations M S , M R) due to piezophase degradation, which is presumably associated with a change in the cations distribution over A and B sublattices of the spinel structure. [ABSTRACT FROM AUTHOR]

In this paper, TiN coatings with grain sizes of 54.8 nm, 68.8 nm, 91.5 nm and 136.9 nm was prepared on the aluminum alloy by extending the coating deposition duration. The mechanical performance under nanoindentation and sand erosion were evaluated. The results show that there is a positive correlation between the hardness of the TiN coating and the grain size. Under the shear stress, the primary mechanism governing the mechanical behavior of the TiN coating is grain boundary sliding when the grain size is less than 70 nm. However, when the grain size surpasses 90 nm, the mechanical response shifts towards the emergence of shear bands and lateral cracks. During nanoindentation loading, TiN coatings with different grain size shows amorphous transformation. Sand erosion experiments demonstrate that refining the grain structure enhances the coordination capability of the TiN coating during plastic deformation, leading to a substantial increase in the amount of sand needed to initiate coating cracks. Simultaneously, the augmentation in the quantity of grain boundaries enhances the TiN coating's capacity for coordinating during plastic deformation, ultimately bolstering its resistance to crack propagation and erosion. [ABSTRACT FROM AUTHOR]

This study aims to enhance the surface toughness and overall performance of arc-shaped nail teeth, which are vital components of presowing film-recovery machinery. Laser cladding technology was employed to deposit Ni60A/Cr 3 C 2 composite coatings with the rare-earth oxide Y 2 O 3 onto 60Si 2 Mn steel surfaces. The effects of different amounts of Y 2 O 3 on the wear resistance of Ni60A/Cr 3 C 2 composite coatings were evaluated. Scanning electron microscopy (SEM), X-ray diffraction, X-ray photoelectron spectroscopy, and 3D morphological analysis were used to investigate the microstructure, microhardness, elemental distribution, and tribological properties of the coatings. The ideal amount of Y 2 O 3 to add to the mixtures to enhance the wear resistance was determined. The results showed that the coating containing 1.5% Y 2 O 3 and Ni60A/Cr 3 C 2 composite powder exhibited superior overall performance. Coatings with different amounts of added Y 2 O 3 exhibited similar phase compositions, mainly consisting of γ-Ni-based, Ni 2 Si, M 7 C 3 (M = Cr, Mn), and M 23 C 6 -strengthened phases. SEM analysis revealed that the coating with 1.5% Y 2 O 3 exhibited excellent metallurgical bonding with the substrate. In addition, the coating exhibited finer grains, increased density, a more uniform distribution of coating elements, and a microhardness of 990 HV. Fewer grooves and smoother abrasions were observed after the wear test. The wear amount and depth were 14 × 10−4 g and 8.97 μm, which were 22.2% and 55.4% lower than the coating without added Y 2 O 3 , respectively. The tribological behavior indicated that adding the appropriate amount of Y 2 O 3 facilitated the grain boundary consolidation while enhancing the adhesive properties of the oxide film, thereby increasing the wear resistance of the coating. [ABSTRACT FROM AUTHOR]

The ceramic samples of Y 1-x Ca x Fe 0.5 Co 0 · 5 O 3 (x = 0.15, 0.25, 0.35) has been synthesized using solid-state reaction method. These samples exhibited orthorhombic perovskite structure and belonged to the Pbnm space group. X-ray analysis confirmed that Ca2+ ions replaced Y3+ ions at the A-site of perovskite structured YFe 0 · 5 Co 0 · 5 O 3 compound, while XPS studies confirmed the oxidation states of the constituent atoms. SEM micrographs and Williamson-Hall analysis showed that the crystallite size reduces with increasing Ca content, resulting in a strain-free, accommodated and stable microstructure. Complex impedance spectroscopic investigations established that the dispersion behaviors exhibited by the samples are due to Interfacial and Bulk polarizations. These phenomena are attributed to the accumulation of space charges and the hopping of electrons, respectively. Study further explore the semiconducting nature and negative temperature coefficient behavior of the material. Nyquist plots showed that grain interior is the major contributor to the conduction mechanism, while grain boundaries playing a secondary role. Correlated Barrier Hopping (CBH) has emerged as a suitable model to elucidate the conduction mechanism. The conduction process facilitated by CBH could potentially account for the observed negative permittivity in the material. [ABSTRACT FROM AUTHOR]