Properties Of Related Materials Research Articles

Role of W-site substitution on mechanical and electronic properties of cubic tungsten carbide

In order to understand the role of W-site substitution on properties of cubic tungsten carbide (-WC), we have investigated the structural, mechanical, and electronic properties of WXC2 (X = Si, Sc, Ti, V, Cr, Ge, Y, Zr, Nb, Mo, Ru, Rh, Pd, Ag, Cd, Sn, Hf, Ta, Re, Os, Ir, Pt, Th, U) using first principles calculations based on density functional theory, within generalized gradient approximation. The structural optimization has carried out for all these compounds using force as well as stress minimization. The optimized structural parameters for experimentally known compounds are in good agreement with the available x-ray diffraction measurements and structural parameters for nineteen WXC2 compounds are newly predicted. The W-site substitution of the above-listed elements into -WC reduces the symmetry of the primitive lattice to tetragonal structure. The heat of formation () and the mechanical stability studies are carried out to investigate the stability of these systems. The single-crystal elastic constants cij, elastic moduli of the polycrystalline aggregates, anisotropy in elastic constants and related properties of the WXC2 materials have calculated and discussed in detail. The hardness of the above materials is predicted using two different criteria, based on the softest elastic mode as well as the Pugh’s modulus ratio. There is a correlation in the hardness predicted from these two approaches except in the case of -WC. The chemical bonding interaction between the constituents is analysed using the density of states, crystal orbital Hamiltonian population, and charge density for selected systems. All these compounds are predicted to be metal and our calculations suggest that W-site substitutions do not improve the hardness of -WC. However, from the heat of formation studies, we have identified five new stable compounds such as CrWC2, NbWC2, ScWC2, YWC2, and UWC2 with reasonably good hardness and those need experimental verifications.

Modelling the moisture redistribution in concrete floors with screed and flooring material with varying properties

Flooring materials and adhesives can be degraded by high pH moisture from e.g. concrete. One way to avoid this degradation, is to dry the concrete and the screed to a sufficient moisture state prior to application of the flooring material. One way to evaluate the moisture state in the materials sensitive to high pH moisture is to calculate the redistribution of moisture in the flooring system from application and onwards. The calculations require substantial knowledge in both moisture related material properties and mass transport calculations in porous materials. The availability of more user-friendly calculations tools stresses the need for a common methodology for both performance and documentation of the calculations. Several input parameters are needed for the calculation, such as boundary conditions, initial moisture distribution and material properties. The most important material properties are the water vapor sorption isotherms (desorption, absorption and scanning) and moisture transport coefficients. This study is investigating the sensitivity of the moisture redistribution calculations to different input parameters, and assumptions needed for the calculation. It is also clarifying what relative humidity intervals that are relevant for different materials in the system and identifying a required accuracy in the different material properties. A first part of round-robin studies with selected cases has been performed to evaluate difference between calculations tools and users.

Mechanically Tunable Spontaneous Vertical Charge Redistribution in Few-Layer WTe2

Broken symmetry is often the essence of exotic properties in condensed matters. WTe2 exceptionally takes a non-centrosymmetric crystal structure in the family of transition-metal dichalcogenides and exhibits novel properties, such as the nonsaturating magnetoresistance and ferroelectric-like behavior. Herein, using the first-principles calculation, we show that unique layer stacking in WTe2 generates surface dipoles in few-layer WTe2. The surface dipoles are tunable and switchable using the interlayer shear displacement. This could explain the ferroelectric-like behavior recently observed in atomically thin WTe2 films. In addition, we reveal that exfoliation of the surface layer flips the out-of-plane spin textures. The presented results will aid in the deeper understanding, manipulation, and further exploration of the physical properties of WTe2 and related atom-layered materials for applications in electronics and spintronic devices.

Questaal: A package of electronic structure methods based on the linear muffin-tin orbital technique

This paper summarises the theory and functionality behind Questaal, an open-source suite of codes for calculating the electronic structure and related properties of materials from first principles. The formalism of the linearised muffin-tin orbital (LMTO) method is revisited in detail and developed further by the introduction of short-ranged tight-binding basis functions for full-potential calculations. The LMTO method is presented in both Green’s function and wave function formulations for bulk and layered systems. The suite’s full-potential LMTO code uses a sophisticated basis and augmentation method that allows an efficient and precise solution to the band problem at different levels of theory, most importantly density functional theory, LDA+U, quasi-particle self-consistent GW and combinations of these with dynamical mean field theory. This paper details the technical and theoretical bases of these methods, their implementation in Questaal, and provides an overview of the code’s design and capabilities. Program summaryProgram Title: QuestaalProgram Files doi:http://dx.doi.org/10.17632/35jxxtzpdn.1Code Ocean Capsule:https://doi.org/10.24433/CO.3778701.v1Licensing provisions: GNU General Public License, version 3Programming language: Fortran, C, Python, ShellNature of problem: Highly accurate ab initio calculation of the electronic structure of periodic solids and of the resulting physical, spectroscopic and magnetic properties for diverse material classes with different strengths and kinds of electronic correlation.Solution method: The many electron problem is considered at different levels of theory: density functional theory, many body perturbation theory in the GW approximation with different degrees of self consistency (notably quasiparticle self-consistent GW) and dynamical mean field theory. The solution to the single-particle band problem is achieved in the framework of an extension to the linear muffin-tin orbital (LMTO) technique including a highly precise and efficient full-potential implementation. An advanced fully-relativistic, non-collinear implementation based on the atomic sphere approximation is used for calculating transport and magnetic properties.

Suppression of abnormal grain growth in K0.5Na0.5NbO3: phase transitions and compatibility

This work presents the suppression of abnormal grain growth in bulk ceramic K0.5Na0.5NbO3 (KNN). The suppression is enabled by precise control of the starting powder morphology through match of milling and calcination duration. A comparative temperature-dependent analysis of the resulting sample morphology, phase transitions and related electronic material properties reveals that abnormal grain growth is indeed a major influence in material property deterioration, as has theoretically been suggested in other works. However, it is shown that this abnormal grain growth originates from the calcined powder and not from sintering and that all subsequent steps mirror the initial powder morphology. In specific, the results are discussed with respect to the predictions of the compatibility theory and microstructure. Despite the material’s multi-scale heterogeneity, the suppression of abnormal grain growth allows for the achievement of significantly improved functional properties and it is reported that this development is correctly predicted by the compatibility theory within the borders of microstructural integrity. It could be demonstrated that functional fatigue is strongly minimised, while thermal and electronic properties are improved when abnormal grain growth is suppressed by powder morphology control.

Synergistic Chemotherapy and Photodynamic Therapy of Endophthalmitis Mediated by Zeolitic Imidazolate Framework-Based Drug Delivery Systems.

Endophthalmitis, derived from the infections of pathogens, is a common complication during the use of ophthalmology-related biomaterials and after ophthalmic surgery. Herein, aiming at efficient photodynamic therapy (PDT) of bacterial infections and biofilm eradication of endophthalmitis, a pH-responsive zeolitic imidazolate framework-8-polyacrylic acid (ZIF-8-PAA) material is constructed for bacterial infection-targeted delivery of ammonium methylbenzene blue (MB), a broad-spectrum photosensitizer antibacterial agent. Polyacrylic acid (PAA) is incorporated into the system to achieve higher pH responsiveness and better drug loading capacity. MB-loaded ZIF-8-PAA nanoparticles are modified with AgNO3 /dopamine for in situ reduction of AgNO3 to silver nanoparticles (AgNPs), followed by a secondary modification with vancomycin/NH2 -polyethylene glycol (Van/NH2 -PEG), leading to the formation of a composite nanomaterial, ZIF-8-PAA-MB@AgNPs@Van-PEG. Dynamic light scattering, transmission electron microscopy, and UV-vis spectral analysis are used to explore the nanoparticles synthesis, drug loading and release, and related material properties. In terms of biological performance, in vitro antibacterial studies against three kinds of bacteria, i.e., Escherichia coli, Staphylococcus aureus, and methicillin-resistant S. aureus, suggest an obvious superiority of PDT/AgNPs to any single strategy. Both in vitro retinal pigment epithelium cellular biocompatibility experiments and in vivo mice endophthalmitis models verify the biocompatibility and antibacterial function of the composite nanomaterials.

(Invited) Epitaxial Lift-Off of GaN and Related Materials for Device Applications

The unique material and transport properties of GaN and related III-N materials have led to their importance in both optoelectronic and RF/microwave power amplification applications, as well as to their promise for emerging applications including power control and conversion, harsh-environment and radiation-resistant sensing and signal processing, and biomedical applications. The use of epitaxial lift-off with III-N materials provides an approach that can improve the electrical and thermal performance of electronic and optoelectronic devices, while at the same time reducing cost and dramatically reducing device size and weight. However, in contrast to other III-V material systems, epitaxial lift-off of III-N materials is challenging due to the lack of high-selectivity, high-etch-rate wet etches in this material system. As an alternative, we have explored the use of band gap selective photoelectrochemical (PEC) wet etching to perform epitaxial lift-off of GaN-based materials and devices. By combining the use of a thin pseudomorphic InGaN release layer and KOH electrolyte with high-intensity filtered ultraviolet illumination tuned to generate electron-hole pairs only in the InGaN release layer (and not in the surrounding GaN material), sufficient selectivity and etch rate have been achieved to allow epitaxial lift-off of large-area films [1]. This process has been demonstrated to improve the electrical and thermal performance of Schottky diodes on non-native substrates [2, 3] and high-voltage, high-power pn junctions grown on low-dislocation-density bulk GaN substrates [4-6] without compromising material quality, while also resulting in ultra-thin devices with total thicknesses below 15 µm. The devices show no evidence of additional defects or recombination centers as a result of either the inclusion of the pseudomorphic InGaN release layer in the epitaxial layer structure or the epitaxial lift-off fabrication processing steps. In addition to device performance, device cost can be improved both through potential re-use of the substrate after lift-off [7] and reduction in die size due to improved thermal performance [8]. While demonstrated for power electronics applications, the ability to form high-quality, high-performance III-N based devices in an ultra-thin, flexible form factor may be an enabling technology for additional applications in flexible electronics, displays, wearable electronics, RF/microwave communication systems, and other fields.

Coordination Dynamics and Thermal Stability with Aminal Metallogels and Liquids

In this article, we review a dynamic covalent gel system developed as a high temperature well construction fluid. The key gel/fluid phase changes and related materials properties are addressable via the constitutional and coordination dynamics of the equilibrium and non-equilibrium molecular species comprising the material. The interplay between these species and external stimuli leads to material adaptability. Specifically, the introduction of metal ions into a non-equilibrium hemiaminal gel reverts this phase into a non-equilibrium liquid. When heated, this liquid transforms itself catalytically into the thermodynamically favoured closed-ring polyhexahydrotriazine (PHT) gel product. The temperature stability of different PHT gel formulations is evaluated as a function of the inclusion of various salts. It is possible to revert this thermodynamic PHT gel back into a liquid. This pH dependent transformation depends on the R groups linking the hexahydrotriazines (HTs) to one another. While polyethylene glycol (PEG) based PHT gels revert to liquids with water and mild protonation conditions, in comparison, polypropylene glycol (PPG) based gels require stronger acid conditions with heat, or a different more nucleophilically driven ring-opening mechanism by, for example, phosphines. The covalent dynamic chemistry in this chemical system gives way to many possible applications in addition to the high temperature solution-gelation (sol-gels) for which it has been primarily designed.

Strong plasmon-molecule coupling at the nanoscale revealed by first-principles modeling

Strong light-matter interactions in both the single-emitter and collective strong coupling regimes attract significant attention due to emerging applications in quantum and nonlinear optics as well as opportunities for modifying material-related properties. Exploration of these phenomena is theoretically demanding, as polaritons exist at the intersection between quantum optics, solid state physics, and quantum chemistry. Fortunately, nanoscale polaritons can be realized in small plasmon-molecule systems, enabling treatment with ab initio methods. Here, we show that time-dependent density-functional theory calculations access the physics of nanoscale plasmon-molecule hybrids and predict vacuum Rabi splitting. By considering a system comprising a few-hundred-atom aluminum nanoparticle interacting with benzene molecules, we show that cavity quantum electrodynamics holds down to resonators of a few cubic nanometers in size, yielding a single-molecule coupling strength exceeding 200 meV due to a massive vacuum field of 4.5 V · nm−1. In a broader perspective, ab initio methods enable parameter-free in-depth studies of polaritonic systems for emerging applications.

Enhanced luminescence in Tb3+-doped glass-ceramic scintillators containing LiYF4 nanocrystals

Tb3+ ions single-doped transparent oxyfluoride glass-ceramics (GC) containing LiYF4 nanocrystals were prepared via a conventional high-temperature melt quenching way and subsequent further thermal-treatment. The microstructure and related luminescent properties of the composite materials were studied in detail. It was confirmed by XRD and TEM techniques that the precipitated particles in the glass phase of the GC590-4h sample were LiYF4 nanocrystals having a size of approximately 26 nm. Compared to the PG sample, the luminescence intensity of the GCs at 378 nm light excitation was significantly enhanced and the corresponding lifetime was prolonged. This is because the Tb3+ ions are preferentially enriched in the precipitated low-phonon-energy LiYF4 nanocrystals, which can effectively induce the reduction of non-radiative transitions. It is worth noting that the emission intensity of Tb3+ single-doped GCs containing LiYF4 nanocrystals at 545 nm (5D4→7F5) is also greatly improved (under X-ray excitation). The obtained results indicate that Tb3+ single-doped LiYF4 GC may have the potential to be a novel scintillator applied to X-ray detection for the slow event.

Direct observation of the f–c hybridization in the ordered uranium films on W(110)**Project supported by the National Natural Science Foundation of China (Grant No. 11874330), Science Challenge Project, China (Grant No. TZ2016004), and the National Key Research and Development Program of China (Grant No. 2017YFA0303104).

A key issue in metallic uranium and its related actinide compounds is the character of the f electrons, whether it is localized or itinerant. Here we grew well ordered uranium films on a W(110) substrate. The surface topography was investigated by scanning tunneling microscopy. The Fermi surface and band structure of the grown films were studied by angle-resolved photoemission spectroscopy. Large spectral weight can be observed around the Fermi level, which mainly comes from the f states. Additionally, we provided direct evidence that the f bands hybridize with the conduction bands in the uranium ordered films, which is different from previously reported mechanism of the direct f–f interaction. We propose that the above two mechanisms both exist in this system by manifesting themselves in different momentum spaces. Our results give a comprehensive study of the ordered uranium films and may throw new light on the study of the 5f-electron character and physical properties of metallic uranium and other related actinide materials.

Multiphonon anharmonicity of MgO

The anharmonic lattice dynamics of MgO has been studied at ambient conditions and at high temperatures by infrared spectroscopy and inelastic x-ray scattering measurements combined with density functional perturbation theory calculations. The agreement between the measured phonon energies and widths with ab initio calculated values provides a direct and pertinent test of the validity of advanced theoretical methods. Long observed anharmonic features in the infrared reflectivity find a clear explanation in terms of well-defined multiphonon scattering processes and lattice dynamics peculiarities, also responsible for a significant and sharp reduction of the longitudinal optical phonon lifetime at critical finite wave vectors. Our work highlights the importance of multiphonon scattering processes on the collective dynamics and related material properties.

Analysis of cold compaction for Fe-C, Fe-C-Cu powder design based on constitutive relation and artificial neural networks

The constitutive relations for Fe-C and Fe-C-Cu powder compactions were investigated with the three consitituents: i) powder design parameters, ii) material related properties, and iii) final compaction properties. With the concept of materials informatics, this approach enables to predict the final compaction properties depending on the material conditions. The correlations between powder design parameters (particle size, graphite content, lubricant content, particle size distribution, copper content) and material related properties (ρTap, γ, a, b, n) in Shima-Oyane model were characterized by the compaction experiments and artificial neural network (ANN) model. The ANN model was developed to predict the effect of powder design parameters on the material related properties. The average mean absolute percentage error of predicted material related properties was 2.194%. The final properties (green density, density gradient, effective stress, hydrostatic stress, effective strain, volumetric strain) were calculated by the compaction simulation based on the experimental and predicted material related properties.

Remarkable wettability of highly dispersive rGO ink on multiple substrates independent of deposition techniques

Numerous methods are available for obtaining reduced graphene oxide (rGO), however, the agglomeration of rGO flakes is a major challenge for different applications. Incorporation of additives (as anti-agglomerating chemicals) along with reducing agents modifies the chemical properties of graphene oxide and related carbon materials. Intrinsically, reduced graphene oxide (rGOH) synthesized via hydrazine (reducing agent) agglomerates and exhibits a hydrophobic nature that limits its surface application necessitating the use of surface treatments. The present article describes a process for the formulation of graphene oxide that results in a highly dispersive ink of rGOA using hydrazine as reducing agent and a water based additive composed cationic surfactants (e.g. Hexadecyltrimethylammonium bromide or benzisothiazoline) and anionic surfactants (e.g. Dioctyl sulfosuccinate sodium salt or methylisothiazolinone). The constituent chemicals of the dispersing agent assist in three ways: (i) allow rGO flakes to exist in a highly dispersive form, (ii) act as binder via cross linking with the carboxylic groups, and (iii) enhance the wettability of the rGO ink on a variety of substrates including glass, SiO2, PDMS etc, without any surface treatment, independent of applying techniques say spin coating, dip coating, doctor blade, etc. Thus, the proposed chemical recipe is an attractive procedure to obtain rGOA ink with high wettability owing to its simplicity, low cost and eco-friendly nature.

Tensile strength performance with determination of the Poisson‘s ratio of additively manufactured AlSi10Mg samples

AbstractAdditive manufacturing of metals is a key technology and an emerging industrial sector enabling the manufacture of highly specialized and advanced components. It's outstanding advantages are the geometric flexibility and the elimination of tools compared to conventional manufacturing techniques. However, multiple directional dependencies lead to an anisotropic material behaviour, rendering the material description more complicated. Samples used for this study were fabricated from the age‐hardenable alloy AlSi10Mg, focusing on fluctuating material properties in relation to differing built orientations. In addition, the effect of thermal post treatment was considered. Comprehensive tensile tests employing a lateral strain sensor were performed, in order to determine the transverse contraction during loading and to quantify directional dependencies. The Young's modulus varied between 66 GPa and 68 GPa, however the Poisson's ratio ranged between 0.31 and 0.39. Investigations on the fractured faces by means of scanning electron microscopy investigations were also part of this study.

A new method for an old topic: Efficient and reliable estimation of material bulk modulus

Bulk modulus is a key material property which provides fundamentals on the chemical bonding nature of a material as well as for deriving other related material properties, such as Young’s modulus and Grüneinsen constant. Traditional numerical methods of estimating bulk modulus often involve layers of approximations and cost considerably. In this work, we propose a novel and efficient numerical framework to estimate bulk modulus using the ab initio calculated data. Based on the generalized polynomial chaos expansion (gPC) method, our approach does not impose any physical priori and is mathematically rigorous and versatile. We have demonstrated the reliability and efficiency of the proposed method by estimating the bulk modulus of Ti3SiC2 and Sb2Te3 with comparison to conventional methods.

Effects of Hydroforming Process on Fatigue Life of Reinforced S-Shaped Bellows

Reinforced s-shaped bellows, which can withstand high pressure, is a kind of typical reinforced metal bellows. The reinforced s-shaped bellows mainly uses the hydroforming process, and the forming process is a severe plastic deformation process. The hydroforming process and its effects on the fatigue life of reinforced s-shaped bellows were discussed in the present study. Different levels of plastic strain and wall thickness thinning were detected in the hydroforming process. The maximum plastic strain can reached 32%, while the maximum wall thickness thinning ratio is 20%, which occurs on the wave peak. Mechanical characteristics of reinforced s-shaped bellows were discussed considering the effects of hydroforming process. The maximum stress appears on the upper and lower ends, which is the weak part of the structure. Fatigue life of the reinforced s-shaped bellows was analyzed based on the modified Manson-Coffin method. Mechanical properties of related materials, which can be more accurate consideration the effects of hydroforming process, were tested under the pre-plastic deformation. Fatigue life analysis of reinforced s-shaped bellows was carried out and the effects of hydroforming process were discussed. The hydroforming process will lead to a decline in fatigue life, which needs to be considered well in the structural design and analysis. Keywords: Reinforced s-shaped bellows, Hydroforming process, Fatigue life, Mechanical characteristics.

PROPOSAL FOR A EUROPEAN METROLOGY NETWORK ON BIOLOGICAL IONISING RADIATION EFFECTS.

Progress in the field of ionising radiation (IR) metrology achieved in the BioQuaRT project raised the question to what extent radiobiological investigations would benefit from metrological support of the applied methodologies. A panel of experts from the medical field, fundamental research and radiation protection attended a workshop at Physikalisch-Technische Bundesanstalt to consult on metrology needs related to biological radiation effects. The panel identified a number of metrological needs including the further development of experimental and computational techniques for micro- and nanodosimetry, together with the determination of related fundamental material properties and the establishment of rigorous uncertainty budgets. In addition to this, a call to develop a metrology support for assisting quality assurance of radiobiology experiments was expressed. Conclusions from the workshop were presented at several international conferences for further discussion with the scientific community and stakeholder groups that led to an initiative within the metrology community to establish a European Metrology Network on biological effects of IR.

Poly(urethane-acrylate) aerogels from the isocyanurate trimer of isophorone diisocyanate

Poly(urethane acrylate) aerogels were synthesized from radical polymerization of a dendritic monomer having an isocyanurate-based rigid/aliphatic core, urethane linkages and nine terminal acrylate groups. The rigidity of the core comes from the triisocyanate, an isophorone diisocyanate trimer (IPDI). The material properties of those aerogels were compared to the properties of related literature materials derived from triisocyanates with flexible/aliphatic or rigid/aromatic cores, bearing (a) three, or (b) nine terminal acrylate groups. Data support that material properties such as the primary particle size and the BET surface areas are determined mainly by the degree of crosslinking (i.e., the monomer multifunctionality), while the molecular rigidity vs flexibility of the triisocyanate core plays only a secondary role. Addition of ethylene glycol dimethacrylate (EG) in the sol as a chain extender increased the hydrophilicity of the aerogels and their ability to absorb water.

Dielectric relaxation and electrical properties of Bi2.5Nd0.5Nb1.5Fe0.5O9 ceramics

Abstract Aurivillius single-phase Bi2.5Nd0.5Nb1.5Fe0.5O9 (BNNF) ceramics was synthesized via solid state mixed oxide sintering method. Electrical properties of the samples were intensely studied in a wide range of temperature (25 °C–650 °C). Dielectric behaviors were investigated by dielectric and impedance spectroscopies in the range (40 Hz−10 MHz) of frequency. Single dielectric relaxation was observed due to the grains contribution. The phase transition temperature (TC) was noticed at ∼270 °C. Kinetic analysis of dielectric data was used to understand the possible relaxation-conduction behaviors in the ceramics. Above ∼250 °C, relaxation and conduction of the ceramics was assigned to the motion of ionized oxygen vacancies. The Aurivillius ceramics has promising industrial applications in dielectric capacitors and piezoelectric transducers due to low leakage below ∼200 °C. The results could be valuable for designing and/or modifying properties of BNNF related materials.