Atomic Packing Density Research Articles

Effect of grain size and orientation on magnetron sputtering yield of tantalum

The electron beam melting (EBM) technique was employed to prepare ultra-highly pure (99.999 wt%) Tantalum (Ta) cast ingot for application in chips. Subsequently, the Ta cast ingot were forged, rolled, and annealed with different durations to gain three different grain sizes (centimeter scale, 99.8 μm, and 36.7 μm). Sputtering experiments conducted under identical conditions revealed that the rolled target (36.7 μm) film deposition rate was increased by 60.6 % compared to the cast ingot target with a centimeter-scale grain size (columnar crystal). Ta targets with a fine grain size and homogeneous distribution demonstrate superior film deposition performance. The sputtering rate is directly related to the atomic packing density of grains. The (111)-oriented grains of BCC targets (Ta target) exhibit sputtering resistance, and the order of sputtering rate of Ta atoms was S(101) > S(001) > S(111).

Enhancing structural strength and microwave dielectric properties of the Ba4(Sm1-xCex)9.33Ti18O54 ceramics

Herein, microwave dielectric ceramics of the Ba4Sm9.33Ti18O54 ceramics are substituted at A sites by partially replacing Sm at A1 sites with Ce, and the effects of ionic substitution at A sites on ceramic crystal structure and microwave dielectric properties are investigated. The Ba4(Sm1-xCex)9.33Ti18O54 (BSCT) ceramics prepared through the solid phase method has a typical tungsten–bronze structure, and its lattice spacing increases gradually with the increase in Ce content x. This increase is reflected in the increase in the cell volume and growth of ceramic grains. However, the excess Ce after Ce content exceeds 0.25 leads to the growth of ceramic grains and increase in porosity between grains, which in turn increases the dielectric loss of the ceramic. Under optimal sintering conditions, the ceramic crystal has a maximum atomic packing density of x = 0.25, which corresponds to its most stable structural properties, and the highest Q × f value of 9013 GHz. Raman spectroscopy results indicate that in titanium oxygen octahedrons, an increase in Ce substitution can effectively weaken the bending and tensile vibration intensities of titanium oxygen bonds, further enhancing structural strength.

Molecular dynamics simulations study on structure and mechanical properties of Na2O–CaO-Al2O3-B2O3-SiO2 glasses with different Al2O3/B2O3 ratio

The structure and mechanical properties of Na2O–CaO-Al2O3-B2O3-SiO2 glass were simulated using molecular dynamics simulations, with Al2O3 replacing B2O3. The simulated elastic modulus (E) increases while the fracture toughness (KIc) decreases, consistent with the experimental findings. The increase in Al2O3/B2O3 enhances the proportion of [AlO4] in the glass network, while reducing the proportion of [BO4] and [BO3], thereby increasing dissociation energy and atomic packing density, ultimately improving the E of the glass. The fracture process of glasses involves both elastic and plastic deformations. Elastic deformation primarily includes bond length extension, bond angle bending, and changes in coordination numbers of Ca2+ and Na+. Plastic deformation primarily results from changes in coordination numbers of B3+ and Al3+ during stretching, with reduced [BO3] and [BO4] decreasing the plastic region and subsequently reducing KIc. This study will provide a theoretical basis for adjusting E and KIc values for aluminoborosilicate glass.

Nearly close-packed atomic arrangements in BaTi2O5 glass

Recent advancements in glass synthesis have led to the creation of novel oxide glasses without tetrahedral corner-sharing networks. Of particular interest are glasses with high atomic packing densities, showcasing improved functionalities. Conventional analyses revealed the presence of not only four-coordinated polyhedra but also five- or six-coordinated polyhedra, which are connected via corner-sharing, edge-sharing, or face-sharing linkages. This study adapted the reduced atomic arrangement (RAA) method to analyze densely packed oxide glasses. The RAA method revealed a near-close-packed structure within a 10 Å range throughout BaTi2O5 glass, with Ba2+ and O2− ions arranged accordingly. Moreover, the structural model derived from relaxing the closest-packed arrangement via molecular dynamics simulations faithfully replicated the X-ray diffraction data. These findings suggest that minor deviations from the closest-packed atomic arrangement can initiate glass formation without corner-sharing tetrahedral networks. The RAA method proves highly effective in understanding glass formation mechanisms in unconventional oxide glasses.

Strain-dependent work function of metal surfaces: Insights from first-principles investigation

Establishing a fundamental understanding of the relationship between electronic work function (WF) and applied strain is crucial for the development flexible electrodes of and enhancement of metal corrosion resistance. The underlying mechanisms of this relationship have remained unknown, largely due to inconsistencies from previous studies caused by different strain states and the complex impact of anisotropic surface effects. In this study, we employ first-principles methods to investigate the work functions of strained metal surfaces. Our research findings suggest that lateral strain states significantly affect the WF, while strain perpendicular to the surface has minimal influence. Through subjecting the metal surface to linear elastic deformation, we establish a canonical relationship between the work function and strain. Further comparison of work functions under biaxial strain indicates that surfaces with high atom packing density exhibit greater susceptibility to strain. The mechanism behind the strain-dependent WF is attributed to the interplay of bulk electronic structure and surface dipole effects, which. These effects are influenced by volume changes and the redistributedion of charge density. To this end, we propose an effective strain-induced approach for engineering the WF of metal electrode is proposeds, with potential applications in other various materials.

Some strange things about the mechanical properties of glass

Glasses and crystals from the same chemical system mostly share the same interatomic bond strength. Nevertheless, they differ by the arrangement of bonds in space, which gives birth to different atomic packing efficiencies. We show in this review that as far as the elastic moduli and hardness are concerned, the atomic packing density predominates over the bond strength. The shear modulus of crystalline phases is usually much larger than the one of glasses with the same stoichiometric composition, thanks to a more efficient packing of atoms in the former. In contrast, the increase in hardness is quite limited, likely because of the additional contribution of dislocation activity to the deformation processes beneath the indenter in the case of crystals (shear plasticity). We also show that the occurrence of chemical heterogeneities (weak channels) at the mesoscopic scale in glasses, which is often associated with the lack of long range atomic ordering, promotes easy fracture paths and is responsible for the low toughness and fracture surface energy.

Room temperature nanoindentation creep behavior of CoNiCrMo-based high entropy amorphous alloy coatings prepared by HVAF

The present study aimed to explore the creep behavior of CoNiCrMo-based high entropy amorphous alloy coatings at room temperature using nanoindentation creep experiments. The coatings were subjected to different loading rates to assess their performance. The findings indicate that the high entropy effect of the (Co0.33Ni0.33Cr0.23Mo0.1)80-xNbx(B0.7Si0.3)20 (x = 0, 2 and 4 at. %) high entropy amorphous alloy coatings has a notable impact on the creep resistance and facilitates a uniform plastic deformation during creep. The shear transition zone (STZ) size and the free volume content during creep deformation exhibit an increase in response to the concentration of Nb. This phenomenon can be attributed to the elevated atomic packing density and the hindered movement of atoms resulting from the incorporation of Nb. Nb content has a favorable impact on the creep stress index, increasing creep stress. Also, the high concentration of Nb is found to mitigate the propensity of the stress exponent to drop with increasing loading rates. The high entropy effect of the as-sprayed coatings promotes high creep resistance and homogenous creep deformation.

The structure dependence of grain boundary passivation of Alloy 690 in high temperature water

The oxidation behavior of grain boundaries (GBs) was investigated on Alloy 690 after exposure to simulated pressurized water reactor primary water. The tendency to form passive film above GB is positively related to Cr diffusivity along GB which is determined by GB structure. Highly-ordered GB like twin boundary is subject to penetrative oxidation as Cr diffusivity is very low. GBs with misorientation angle θ ≤17.4° can't support fast diffusion of Cr either and also show penetrative oxidation. When θ ranges between 17.4° and 28.7°, Cr diffusivity is enhanced a little and GB shows unstable passivation. Meanwhile, the Cr diffusivity along GB is also related to the atomic packing density of GB planes. GB with higher atom packing density exhibits lower Cr diffusivity and deeper intergranular oxide depth. As θ increases above 28.7°, Cr diffusion is fast enough to support the formation of protective film above GB.

Effects of Li+ enrichment on the structure and microwave dielectric properties of LiMgPO4 ceramics

In this study, Li+-enriched Li1+xMgPO4 ceramics were prepared at 875–1025 °C by the solid-phase methods. The effects of Li+-enriched on the sintering characteristics, phase composition, crystal structure, and microwave dielectric properties of LiMgPO4 ceramics were investigated. As x increased, the relative density initially increased and then marginally decreased. Raman spectroscopy revealed that P–O bonds significantly affected the dielectric properties. Further, the values of Q × f first increased and then decreased owing to the combined effects of the full width at half maximum of peak v1 and atomic packing density. Moreover, optimal Li+ enrichment reduced the distortion of the Li/PO4 tetrahedron, thereby increasing Q × f. Li1.0125MgPO4 ceramics exhibited the best dielectric properties when sintered at 950 °C, yielding εr = 7.14, Q × f = 95039 GHz, and τf = −56.1 ppm/°C. Thus, Li1+xMgPO4 ceramics can be potentially used in various microwave communication applications.

Role of rare earth elements addition in enhancing glass-forming ability and magnetic softness of a Co75B25 metallic glass: Theoretical prediction and experimental verification

The effects of light/heavy rare earth (L/HRE) elements addition on local atomic structures, glass-forming ability (GFA), and soft magnetic properties of a Co75B25 metallic glass (MG) were comprehensively investigated using theoretical prediction and experimental verification methods. Ab initio molecular dynamics (AIMD) simulations based on density functional theory (DFT) calculations revealed that the Co-RE-B (RE = La, Sm, Gd, and Y) MGs exhibit unique structural heterogeneities, with B-centered prism units dominating the local atomic structures. Compared to the Co-LRE-B (LRE = La and Sm) MGs, the Co-HRE-B (HRE = Gd and Y) MGs possess stronger bond strengths and higher fractions of icosahedral-like (ico-like) units, leading to remarkable enhancements in structural stability, fivefold symmetry, atomic packing density, and sluggish diffusion, ultimately resulting in enhanced GFA. Furthermore, the lower magnetic anisotropy energy (MAE) and range of the local loosely packed regions (LLPRs) in the HRE-containing MGs can significantly promote magnetic softness. The theoretical analysis predicts that the MGs containing the HRE possess higher GFA and magnetic softness with the order of Co75B25 < Co71.5La3.5B25 < Co71.5Sm3.5B25 < Co71.5Gd3.5B25 < Co71.5Y3.5B25. These predictions have been successfully verified by the experiments in both local atomic structures and properties, through the in situ high-energy synchrotron X-ray diffraction (HEXRD) characterization, as well as evaluations of thermal and magnetic properties.

Atomic structure, thermal stability and isothermal crystallization kinetics of novel Co-based metallic glasses with excellent soft magnetic properties

In this work, Co66-xFexHf6.5B27.5 (x = 0, 10, 15, 20) metallic glasses (MGs) have been prepared by melt-spinning, and a comprehensive qualitative study including the atomic structure, thermal behavior, crystallization kinetics, and magnetic properties of the MGs is presented. The addition of Fe notably improves the thermal stability of the prepared glasses by increasing the width of the supercooled liquid region (SLR) from 26 K to 55 K. Analysis of the structure factor and the reduced-pair distribution function (PDF) reveal subtle variations in short-range ordering (SRO) and an increase of the atomic packing density of the glassy phase by 20 at% Fe addition. Notable rises in saturation polarization, Js, (from 0.21 T to 0.67 T), Curie point, Tc, (from 315 K to 530 K) and coercivity, Hc, (from 0.5 A/m to 2.5 A/m) are found after Fe alloying. The isothermal crystallization kinetics determined by the Johnson-Mehl-Avrami-Kolmogorov (JMAK) approach demonstrate that the novel Co46Fe20Hf6.5B27.5 MG exhibits a remarkably higher activation energy and a significantly longer incubation time (about 16 min) before crystallization compared to existing Fe-free (x = 0) as well as most other Fe/Co-based MGs. Slight increases in Js (up to 5%) and Tc (about 4.7%), and a remarkable drop in Hc (up to 80%) are achieved for the Co46Fe20Hf6.5B27.5 MG upon isothermal annealing for a period of 3600 s. The attractive features such as high thermal stability, low coercivity of 0.5 A/m, and higher Js (up 0.7 T) compared to many Co-based glasses, make Co46Fe20Hf6.5B27.5 MG a promising soft magnetic material for future applications in power electronics, electric machines, and fabrication of large-size glassy samples by hot consolidation of MG particles.

Molecular dynamics simulations study on structure and properties of CaO–MgO–B2O3–Al2O3–SiO2 glasses with different B2O3/MgO

CaO–MgO–B2O3–Al2O3–SiO2 glasses are of great important in glass fiber industry. In this work, the structures, thermal stabilities, and elastic moduli of the glasses are studied using molecular dynamics (MD) simulations by gradual substitution between B2O3 and MgO. The results show that with the increase of the ratios of B2O3/MgO, aluminum shows complex coordination changes, but the four-coordination aluminum is still the dominating specie. The boron coordination environment does not change significantly with the substitution and the three-coordination boron keeps staying at a high level. The percentages of bridge oxygen and network connectivity (NC) in the glasses increase with the increase of B2O3/MgO ratios, which enhances the glass network and improve the thermal stabilities. The elastic moduli calculated from simulations are in good agreement with the experiments. The study shows that high content of Mg2+ can increase atomic packing density. The introduction of boron brings more [BO3] structures, which further weakens the stiffness of the glass network. Insights of the effect of B2O3/MgO ratios on the structures and properties will facilitate the development of high-performance glass fibers.

Local structural power exponent as an indicator of elastic heterogeneity in glasses

The origin of the nontrivial power-law relationships between atomic packing density and the related structural properties is considered to be a key puzzle in understanding the nature of glasses. Here, we report the direct link between the medium-range structural evolution and elastic heterogeneity by systematically investigating the packing-density-dependent properties of various glasses based on extensive large-scale molecular dynamics simulations. It is shown that the power exponent of the peaks corresponding to the medium-range orders on the pair correlation function converges to the exponent of the first diffraction peak rather than the Euclidean dimension. This exponent can be regarded as an indicator of heterogeneous mechanical properties. The global power-law relationship results from intrinsic mechanical heterogeneity, with the nontrivial power-law response being a local feature. Our finding provides a different perspective on order in disordered materials and sheds some light on the structural-property relationship in glasses.

The structure dependence of oxidation behavior of high-angle grain boundaries of alloy 600 in simulated pressurized water reactor primary water

The intergranular degradation of seven different types of high-angle grain boundaries (HAGBs) were investigated on Alloy 600 after exposure to simulated pressurized water reactor primary water. All boundaries are susceptible to preferential intergranular oxidation (PIO) except for ideal coherent twin boundary. Diffusion induced grain boundary migration (DIGM) normally occurs and its depth is positively correlated with the PIO extent. Interestingly, the PIO susceptibility is independent on the grain boundary misorientation angle or Σ value, but related to the grain boundary atom packing density (GBAPD). Grain boundaries with higher GBAPD values show higher PIO resistance as the element diffusion is slower.

The Nanoscale Density Gradient as a Structural Stabilizer for Glass Formation

The rapid cooling of a metallic liquid (ML) results in short-range order (SRO) among the atomic arrangements and a disordered structure in the resulting metallic glass (MG). These phenomena cause various possible features in the microscopic structure of the MG, presenting a puzzle about the nature of the MGs’ microscopic structure beyond SRO. In this study, the nanoscale density gradient (NDG) originating from a sequential arrangement of clusters with different atomic packing densities (APDs), representing the medium-range structural heterogeneity in Zr60Cu30Al10 MG, was characterized using electron tomography (ET) combined with image simulations based on structure modeling. The coarse polyhedrons with distinct facets identified in the three-dimensional images coincide with icosahedron-like clusters and represent the spatial positions of clusters with high APDs. Rearrangements of the different clusters according to descending APD order in the glass-forming process are responsible for the NDG that stabilizes both the supercooled ML and the amorphous states and acts as a hidden rule in the transition from ML to MG.

A new type of gradient structure FeCoCrNiWMo high entropy alloy layer by plasma solid-state surface metallurgy

In this paper, the FeCoCrNiWMo HEA layer with metallurgical bonding and gradient structure was successfully prepared by plasma solid-state surface metallurgy for the first time. The microstructure, composition, growth and deposition kinetics of HEA layer was studied by XRD, SEM and EDS. The results show that the FeCoCrNiWMo HEA layer consists of HCP and FCC phase. In the equipotential mode, the high vacancy concentration gradient layer can't be formed continuously on the substrate surface. In addition, the serious lattice distortion and the increase of atomic packing density caused by different atomic sizes decrease the density of vacancy formation. So the composite strengthening layer structure of HEA layer (deposit layer + diffusion layer) is formed on the substrate surface instead of conventional alloying layer. According to Boltzmann's hypothesis, the entropy value of calculating the surface mixing entropy of HEA layer is >1.5 R, which accords with the definition of high-entropy alloy. Compared with the substrate, the wear resistance and high-temperature oxidation resistance of the HEA layers are improved to some extent and the wear mechanism of substrate and HEA layers is mainly abrasive wear, which is accompanied by adhesive wear and oxidation wear. The results show that it is reasonable and feasible to prepare a new type metallurgical bonding and gradient structure of wear resistant and high-temperature oxidation resistant HEA layer by plasma solid-state surface metallurgy.

Mathematical modeling of the metrical parameters of hexagonal close-packed metalls

The electronic, magnetic, mechanical and other properties of crystalline substances are due to the feature of their structure — the periodicity and symmetry of the lattice, therefore, the determination of the metrical parameters is an important stage in the study of the characteristics of such materials. The paper considers a number of metals having a crystal lattice of the hcp structural type (hexagonal close packing) – beryllium, cerium, cobalt, dysprosium, erbium, gadolinium, hafnium, holmium, lanthanum, lutetium, magnesium, neodymium, osmium, praseodymium, rhenium, ruthenium, scandium, terbium, titanium, thallium, thulium, yttrium, zirconium. The paper shows the application of the annealing simulation algorithm to find the metric parameters of the materials under consideration using the dense packing model, which is widely used in crystallographic calculations. The own software implementation of the annealing simulation algorithm presented in the paper makes it possible to determine the coordinates of the atoms included in the unit cell of the crystal lattice, to calculate the lattice constants and the packing density of atoms in the cell of the crystal of the hcp structural type, using the given chemical formula and space symmetry group. These structural characteristics can be used as input parameters in modeling the electronic, magnetic, and other properties of the considered materials. The paper compares the values of the crystal lattice constants obtained as a result of numerical simulation with published data.

Impact of Y2O3 on structural, mechanical and nonlinear optical properties of CrO3-Na2O-B2O3 glasses

Herein, we investigate the effects of transition metal (Cr3+), alkali (Na1+), and rare earth (Y3+) ion doping on the structural, mechanical, and nonlinear optical properties of borate glass. The structural parameters revealed peculiar behaviors. The total ions concentrations values decreased from 2.13 × 1022 cm−3 for 0 mol% of Y2O3 to 2.04 × 1022 cm−3 for 5 mol% of Y2O3. The atomic packing density parameter (APD) values decreased from 67 % for 0 mol% of Y2O3 to 62 % for 5 mol% of Y2O3 additions. The mechanical parameters such as Young, shear, and bulk moduli showed decreased behaviors with further Y2O3 additions. The linear and nonlinear optical properties, such as refractive index, third-order nonlinear susceptibility, nonlinear refractive index, metallization criterion, average electronegativity, electronic polarizability, and optical basicity, were evaluated. The linear and nonlinear refractive indices showed increasing behaviors with further Y2O3 additions. These increased behaviors were attributed to the increased content of nonbridging oxygens with more Y2O3 additions. The present glasses have metallization criterion values between 0.377 and 0.387, which are optimal for use in nonlinear optical devices.

Contact-Mediated Retinal-Opsin Coupling Enables Proton Pumping in Gloeobacter Rhodopsin.

When a chromophore embedded in a photoreceptive protein undergoes a reaction upon photoexcitation, the photoreaction triggers structural changes in the protein moiety that are necessary for the function of the protein. It is thus essential to elucidate the coupling between the chromophore and protein moiety to understand the functional mechanism for photoreceptive proteins, but the mechanism by which this coupling occurs remains poorly understood. Here, we show that nonbonded atomic contacts play an essential role in driving functionally important structural changes following photoisomerization of the chromophore in Gloeobacter rhodopsin (GR). Time-resolved ultraviolet resonance Raman spectroscopy revealed that the substitution of Trp222, which contacts with methyl groups of the retinal chromophore, with a Phe residue reduced the extent of structural change. The proton-pumping activity of the GR mutant was as small as 9% of that of the wild type. Time-resolved visible absorption and resonance Raman spectra showed that the photocycle of the mutant proceeded to the L intermediate following the all-trans to 13-cis photoisomerization step but did not result in the deprotonation of the chromophore. The present results demonstrate that the atomic contacts between the chromophore and the Trp222 side chain induce the structural changes necessary for proton transfer. The requirement for dense atomic packing in a protein structure for the efficient propagation of structural changes through a coupling mechanism is discussed.

Mechanical properties of oxynitride glasses

AbstractOxynitride glasses combine a high refractoriness, with Tg typically &gt;850°C, and remarkable mechanical properties in comparison with their parent oxide glasses. Their Young's modulus and fracture toughness reach 170 GPa and 1.4 MPa m.5, respectively. Most reports show good linear relationships between glass property values and nitrogen content. There is a clear linear dependence of Young's modulus and microhardness on fractional glass compactness (atomic packing density). They also have a better resistance to surface damage induced by indentation or scratch loading. The improvements stem from the increase of the atomic network cross‐linking—because of three‐fold coordinated nitrogen—and of the atomic packing density, despite nitrogen being lighter than oxygen and the Si–N bond being weaker than the Si–O bond. For constant cation composition, viscosity increases by ∼3 orders of magnitude as ∼17 eq.% oxygen is replaced by nitrogen. For rare earth oxynitride glasses with constant N content, viscosity, Young's modulus, Tg, and other properties increase with increasing cation field strength (decreasing ionic radius). Research continues to find lighter, stiffer materials, including glasses, with superior mechanical properties. With higher elastic moduli, hardness, fracture toughness, strength, surface damage resistance, increased high temperature properties, oxynitride glasses offer advantages over their oxide counterparts.