Fundamental Material Properties Research Articles

A case study of using x-ray Thomson scattering to diagnose the in-flight plasma conditions of DT cryogenic implosions

The design of inertial confinement fusion ignition targets requires radiation-hydrodynamics simulations with accurate models of the fundamental material properties (i.e., equation of state, opacity, and conductivity). Validation of these models is required via experimentation. A feasibility study of using spatially integrated, spectrally resolved, x-ray Thomson scattering measurements to diagnose the temperature, density, and ionization of the compressed DT shell of a cryogenic DT implosion at two-thirds convergence was conducted. Synthetic scattering spectra were generated using 1D implosion simulations from the LILAC code that were post processed with the x-ray scattering model, which is incorporated within SPECT3D. Analysis of two extreme adiabat capsule conditions showed that the plasma conditions for both compressed DT shells could be resolved.

A continuum modeling study on the electrochemical performance and stability of solid oxide cells and oxygen permeation membranes

The structure, materials and transport kinetics of solid oxide cells (SOCs) and oxygen permeation membranes (OPMs) are quite similar, but a unified and explicit model is lacking. Here, a continuum model for evaluating the electrochemical performance and stability of SOCs and OPMs is developed based on linear irreversible thermodynamics. The oxygen partial pressure at the electrode/electrolyte interface is used to evaluate the stability of SOCs and OPMs, and is calculated by considering the gas exchange at the electrode/electrolyte interface and the mixed ionic and electronic conduction in the electrolyte. The calculation results are verified by the literature data. The effect of fundamental material properties on the SOC's and OPM’s performance under certain operating conditions is studied via parametric scanning. In addition, the stabilities of the SOCs and OPMs are also discussed for various operating conditions. The results show that the open circuit voltage (OCV) and stability of SOCs under open-circuit is not only influenced by the magnitude of resistances of the electrolyte, and the air and fuel electrodes, but also the matching of them. Since the OPM can be regarded as the SOC under the open-circuit condition, the present model is also applicable for calculating the oxygen permeation flux. It is shown that the oxygen permeability is increased by lowering the OCV of the OPM. Optimization of SOFC’s performance should consider the matching of the electrode and the electrolyte resistances and the effect of resistance on stability. The evaluation of the performance of SOECs should consider the achieved electrolytic current density combing with the Faradic efficiency. Promotion of the ionic and/or electronic conductivity of electrolytes can enhance the stability of SOECs, but should be treated carefully due to the sacrifice of Faradic efficiency.

Properties of AgBiI4 using high through-put DFT and machine learning methods

Silver iodo-bismuthates show promise for optoelectronic and other applications. Within this family of materials, AgBiI4 is a prominent model compound. The complexity of AgBiI4 has prevented a conclusive determination of specific atomic arrangements of metal atoms in the bulk material. Here, we employ high through-put density functional and novel machine learning methods to determine physically relevant unit cell configurations. We also calculate the fundamental properties of the bulk material using newly discovered configurations. Our results for the lattice constant (12.7 Å) and bandgap (1.8 eV) agree with the previous theory and experiment. We report new predictions for the bulk modulus (7.5 GPa) and the temperature-dependent conductivity mass for electrons (m0 at T = 300 K) and holes (7m0 at T = 300 K); these masses will be useful in AgBiI4-based device simulations.

From protonation & Li-rich contamination to grain-boundary segregation: Evaluations of solvent-free vs. wet routes on preparing Li7La3Zr2O12 solid electrolyte

Garnet-type Li7La3Zr2O12 (LLZO) has been recognized as a candidate solid electrolyte for high-safety Li-anode based solid-state batteries because of its electro-chemical stability against Li-metal and high ionic conductivity. Solvent (e.g., isopropanol (IPA)) has been commonly applied for preparing LLZO powders and ceramics. However, the deterioration of the proton-exchange between LLZO and IPA/absorbed moisture during the mixing and tailoring route has aroused less attention. In this study, a solvent-free dry milling route was developed for preparing the LLZO powders and ceramics. For orthogonal four categories of samples prepared using solvent-free and IPA-assisted routes in the mixing and tailoring processes, the critical evaluation was conducted on the crystallinity, surficial morphology, and contamination of as-calcinated and as-tailored particles, the cross-sectional microstructure of green and sintered pellets, the morphology and electro-chemical properties of grain boundaries in ceramics, as well as the interfacial resistance and performance of Li anode based symmetric batteries. The wet route introduced Li-rich contaminations (e.g., LiOH∙H2O and Li2CO3) onto the surfaces of LLZO particles and Li-Ta-O segregations at the adjacent and triangular grain boundaries. The LLZO solid electrolytes prepared through dry mixing in combination with the dry tailoring route without the use of any solvent were found to the optimal performance. The fundamental material properties in the whole LLZO preparation process were found, which are of guiding significance to the development of LLZO powder and ceramic production craft.

Design and Development of Apparatus to Measure Thermal Conductivity of Liquid

- Thermal conductivity is the fundamental material property for characterizing the heat transfer. The measurement of thermal conductivity include the measurement of the heat flux and temperature difference. This study aims to design, fabricate and development a reliable instrument to measure the thermal conductivity. The apparatus is completely different form of thermal conductivity apparatus which has been widely applied in normal laboratory. A literature survey concerning available experiment technique for thermal conductivity measurement was conducted. The level of reliability that based on the accuracy and consistent will be proven by comparing the experimental value with theoretical value. The results obtained certified the aim of work which was to develop the thermal conductivity measurement apparatus suitable for data collection and experimental experience in economic way. Key Words: Thermal conductivity, heat flux

Boundary Conditions and Long-Term Implantation Effects with Cardiovascular Nitinol Implants

Nitinol-based cardiovascular implants are used frequently to treat a wide range of cardiovascular diseases. Accordingly, understanding the durability of these devices once deployed into the geometrically dynamic cardiovascular system is of critical importance. While the fundamental material properties of Nitinol are relatively well understood, the boundary conditions imposed on Nitinol-based devices by the cardiovascular system and the corresponding effects on durability are not as well understood. Moreover, longitudinal studies report mixed long-term outcomes which raises question about long-term durability of cardiovascular implants. Understanding of the physiologic boundary conditions with focus on the regions with high mobility can warrant not only the short-term benefit, but also the long-term success with minimized incidence of implant-driven complications. In this article, Nitinol-based implants for the aortic valve, cerebral arteries, thoracic aorta, renovisceral arteries, and peripheral arteries are considered, research studies characterizing related variations in cardiovascular geometry are detailed, and summaries of available clinical studies reporting on outcomes are provided.

Effect of compressive stress on the intrinsic permeability of concrete

Intrinsic permeability of concrete is a fundamental material property governing its durability and the development of pore pressure during fire exposure. Qualitative studies reported in literature suggests a slight decrease in effective permeability under typical service loading levels. However, the extent of this reduction has not been studied quantitatively in relation to typical observational variance. Moreover, no such results are reported for intrinsic permeability. This study shows that, under typical service compressive stress levels, the reduction in intrinsic permeability can be considered negligible.

Network Relaxation and Cooperativity in Ion Conducting Polymers PEO-Li: An Analysis Based on the BSCNF Model

The understanding of fundamental materials properties is indispensable for the development of functional materials. Some years ago, it has been reported that the fragility in poly (ethylene oxide)-based Li+ ion conductors decreases with the Li+ ion content. The behavior was considered as unexpected and the origin unclear. In the present study, it is shown that the Bond Strength-Coordination Number Fluctuation (BSCNF) model of structural relaxation developed by the present authors provides an explanation to the observed behavior. The analysis based on the BSCNF model indicates that the cooperativity, or the number of correlated structural units involved in the network relaxation decreases with the Li+ ion content.

Deep dive into machine learning density functional theory for materials science and chemistry

Electronic structure simulations enable the calculation of a wide variety of fundamental materials properties. However, they consume a significant portion of scientific HPC resources worldwide. Artificial intelligence and machine learning, which have emerged as a powerful tool for analyzing complex datasets, have the potential to accelerate electronic structure calculations such as density functional theory. The combination of these two fields enables highly efficient simulations at unprecedented scales. In this review, the authors present a comprehensive analysis of research articles in chemistry and materials science that employ machine-learning techniques and outline the current trends at the intersection of these fields.

Strain Effects in Wurtzite Boron Nitride: Elastic Constants, Internal Strain, and Deformation Potentials from Hybrid Functional Density Functional Theory

Boron‐containing III‐nitride heterostructures have recently attracted significant attention for improving the efficiency of visible and UV light emitters. However, the fundamental material properties of wurtzite (WZ) boron nitride (BN) are largely unexplored. Here, highly accurate first‐principles calculations are used to gain insight into internal strain, elastic constants, and electronic band structure deformation potentials. These parameters are key ingredients for simulating, and thus predicting, electronic and optical properties of boron‐containing III‐nitride‐based light emitters. The ab initio calculations show, for instance, that the quasi‐cubic approximation for deformation potentials is a poor approximation for WZ BN.

First-principles prediction of magnetic properties in Fe(Co,Ni)(C,N)0.5 alloys

To explore a candidate for rare-earth-free magnets, the effects of the light elements (C,N) addition on the magnetic properties in FeCo and FeNi ordered alloys were examined using first-principles calculations. Among Fe(Co,Ni)(C,N)0.5 alloys, we found that FeNiC0.5 is the most promising, because its uniaxial magnetic anisotropy constant Ku is expected to be 3.0 MJ/m3 (five times Ku of L10-type FeNi) and the increase in the Curie temperature TC by the addition of C was observed. The mechanism for the enhancement of Ku and TC can be understood by the basic concepts of the physics of magnetism. Despite being nonmagnetic themselves, light elements have the potential to improve the fundamental properties of magnetic materials.

Efficient and Stable FA‐Rich Perovskite Photovoltaics: From Material Properties to Device Optimization

AbstractThe perovskite photovoltaic field has developed rapidly within a decade. In particular, formamidinium (FA)‐rich perovskite allows a broad absorption spectrum, and is considered to be one of the most promising perovskite materials. Great progress has been achieved, and most recorded high‐efficient perovskite solar cells (PSCs) used the FA‐rich perovskite light absorption layer. However, the black α‐phase formamidinium lead iodide (FAPbI3) perovskite easily transforms into an undesirable δ‐phase at a low temperature. Thus, researchers have put a lot of effort into deeply understanding the phase transformation and stabilization mechanism of FA‐rich perovskite. Herein, the fundamental physical properties of FAPbI3 materials, including crystal structure, phase‐transition temperature, charge‐carrier dynamics, etc. are summarized, and establish a complete phase evolution with temperature by reviewing previous reports. The intrinsic and external factors are subsequently discussed for influencing the stability of FAPbI3 perovskite and the remarkable breakthroughs of FA‐rich PSCs in recent years are reviewed. Moreover, a series of strategies to stabilize FA‐rich perovskite is summarized, including but not limited to compositional engineering, passivating engineering, processing engineering, and strain engineering. Finally, several new viewpoints are provided for improving the efficiency and stability of PSCs. This review may be regarded as a reference project for preparing high‐efficient and stable perovskite photovoltaic devices.

Intrinsic strengthening and toughening in hexagonal boron nitride by ripples

Increasing strength (maximum stress until permanent deformation) and toughness (fracture resistance) is crucial in engineering applications for all materials, but improving strength often lowers the material's capacity to deform without fracturing, and vice versa. This conflict passes on uniquely to layered van der Waals materials, which are generally brittle. Here, we report simultaneous strengthening and toughening of monolayer and multilayer hexagonal boron nitride (hBN) by ripples. We show using atomistic simulations that stable ripples of varying sizes, modelled based on our experimental observations, increase the intrinsic crack nucleation toughness of hBN by improving both fracture strain and bond strength through a distortion-mediated mechanism. This effect has been traced to the extent of structural asymmetry at the onset of failure, revealing a potential strategy to bolster the fundamental fracture and strength properties of single-phase van der Waals materials significantly.

Second nearest-neighbor modified embedded atom method interatomic potentials for Na-M−Sn (M = Cu, Mn, Ni) ternary systems

Interatomic potentials for Mn-Sn, Ni-Sn, Na-Cu, Na-Mn, and Na-Ni binary systems and Na-Cu-Sn, Na-Mn-Sn, and Na-Ni-Sn ternary systems have been developed on the basis of the second nearest-neighbor modified embedded-atom method (2NN MEAM) formalism. The potentials can describe various fundamental materials properties such as structural, elastic, thermodynamic, and thermal properties in reasonable agreement with experiments and DFT calculations. It is demonstrated that the potentials can be used for atomistic simulations to understand material phenomena and to search for optimal tin-based alloy anode materials for sodium ion batteries.

Cation disorder engineering yields AgBiS2 nanocrystals with enhanced optical absorption for efficient ultrathin solar cells

Strong optical absorption by a semiconductor is a highly desirable property for many optoelectronic and photovoltaic applications. The optimal thickness of a semiconductor absorber is primarily determined by its absorption coefficient. To date, this parameter has been considered as a fundamental material property, and efforts to realize thinner photovoltaics have relied on light-trapping structures that add complexity and cost. Here we demonstrate that engineering cation disorder in a ternary chalcogenide semiconductor leads to considerable absorption increase due to enhancement of the optical transition matrix elements. We show that cation-disorder-engineered AgBiS2 colloidal nanocrystals offer an absorption coefficient that is higher than other photovoltaic materials, enabling highly efficient extremely thin absorber photovoltaic devices. We report solution-processed, environmentally friendly, 30-nm-thick solar cells with short-circuit current density of 27 mA cm−2, a power conversion efficiency of 9.17% (8.85% certified) and high stability under ambient conditions.

Atomic mechanism of near threshold fatigue crack growth in vacuum

Structural failures resulting from prolonged low-amplitude loading are particularly problematic. Over the past century a succession of mechanisms have been hypothesized, as experimental validation has remained out of reach. Here we show by atomistic modeling that sustained fatigue crack growth in vacuum requires emitted dislocations to change slip planes prior to their reabsorption into the crack on the opposite side of the loading cycle. By harnessing a new implementation of a concurrent multiscale method we (1) assess the validity of long-hypothesized material separation mechanisms thought to control near-threshold fatigue crack growth in vacuum, and (2) reconcile reports of crack growth in atomistic simulations at loading amplitudes below experimental crack growth thresholds. Our results provide a mechanistic foundation to relate fatigue crack growth tendency to fundamental material properties, e.g. stacking fault energies and elastic moduli, opening the door for improved prognosis and the design of novel fatigue resistance alloys.

Heterogeneous thermal conductance of nanoparticle-fluid interfaces: An atomistic nodal approach.

The Interfacial Thermal Conductance (ITC) is a fundamental property of materials and has particular relevance at the nanoscale. The ITC quantifies the thermal resistance between materials of different compositions or between fluids in contact with materials. Furthermore, the ITC determines the rate of cooling/heating of the materials and the temperature drop across the interface. Here, we propose a method to compute local ITCs and temperature drops of nanoparticle-fluid interfaces. Our approach resolves the ITC at the atomic level using the atomic coordinates of the nanomaterial as nodes to compute local thermal transport properties. We obtain high-resolution descriptions of the interfacial thermal transport by combining the atomistic nodal approach, computational geometry techniques, and "computational farming" using non-equilibrium molecular dynamics simulations. We use our method to investigate the ITC of nanoparticle-fluid interfaces as a function of the nanoparticle size and geometry, targeting experimentally relevant structures of gold nanoparticles: capped octagonal rods, cuboctahedrons, decahedrons, rhombic dodecahedrons, cubes, icosahedrons, truncated octahedrons, octahedrons, and spheres. We show that the ITC of these very different geometries varies significantly in different regions of the nanoparticle, increasing generally in the order face < edge < vertex. We show that the ITC of these complex geometries can be accurately described in terms of the local coordination number of the atoms in the nanoparticle surface. Nanoparticle geometries with lower surface coordination numbers feature higher ITCs, and the ITC generally increases with the decreasing particle size.

Evaluation of Elastic Modulus of Crushed Stone Base Layers for Compaction Control

Construction of high-quality crushed stone layers is referred to as “an art and one that is not profusely found today”. Conventional acceptance control procedures only confirm densification of the layer and other fundamental material properties with no direct measurement of strength. As a result of this there appears to be a missing link between design requirements and acceptance control. Slushing is required during the construction process to lock up the aggregate, ensuring stability and a good distribution of the fines through the layer. This study endeavours to confirm whether there is a significant difference in the Elastic Modulus of crushed stone layers before and after the slushing process and to investigate cost effective and appropriate means of controlling this. Preliminary results suggest that poor workmanship can be clearly identified and an increase in Elastic Modulus can be confirmed following the right construction methods and procedures.

Effect of walnut powder reinforcement on the mechanical properties of biodegradable natural flax/hemp fibre-based composites

Biomaterials created from raw materials are gaining appeal in the industrial sector due to their high quality, sustainability, and environmental considerations. Combining two types of fibres may enhance the fundamental properties of organic fibre-reinforced hybrid polymeric materials. Natural fibre-reinforced hybrid composites were created using a compression moulding process, using coir fibre, hemp fibre, polypropylene, and montmorillonite Walnut Powders used in this work. The effects of a fibre blend and vermiculite on mechanical performances and biodegradable characteristics were studied. Both the coir and hemp fibres were alkali-treated to diminish their hydrophilic character before the process. The mechanical attributes of the produced lightweight materials were evaluated by UTM equipment, resulting in improvements following the mixing of fibre and particle inclusion. The composite's good biocompatibility and water absorption capabilities were increased by mixing fibres, but particle additions seemed to have the opposite impact.

Growth and characterization of quaternary-alloy ferromagnetic semiconductor (In,Ga,Fe)Sb

We study the growth and properties of the quaternary-alloy ferromagnetic semiconductor (In0.94−x,Gax,Fe0.06)Sb (x = 5%–30%; the Fe concentration is fixed at 6%) grown by low-temperature molecular beam epitaxy. Reflection high-energy electron diffraction patterns, scanning transmission electron microscopy lattice images, and x-ray diffraction spectra indicate that the (In0.94−x,Gax,Fe0.06)Sb layers have a zinc blende crystal structure without any other second phase. The lattice constant of the (In0.94−x,Gax,Fe0.06)Sb films changes linearly with the Ga concentration x, indicating that Ga atoms substitute In atoms in the zinc-blende structure. We found that the carrier type of (In0.94−x,Gax,Fe0.06)Sb can be systematically controlled by varying x, being n-type when x ≤ 10% and p-type when x ≥ 20%. Characterization studies using magnetic circular dichroism spectroscopy indicate that the (In0.94−x,Gax,Fe0.06)Sb layers have intrinsic ferromagnetism with relatively high Curie temperatures (TC = 40–120 K). The ability to widely control the fundamental material properties (lattice constant, bandgap, carrier type, and magnetic property) of (In0.94−x,Gax,Fe0.06)Sb demonstrated in this work is essential for spintronic device applications.