Changes In Short-range Order Research Articles

Densification mechanism and structural transformation in glass: molecular dynamic simulation

The structure of GeO2 glass is investigated via molecular dynamic simulation. The influence of pressure to the structure of GeO2 glass is due to the change of short-range order, network structure, domain structure and free volume regions. The obtained results show that the structure of GeO2 was formed by a continuous random network of basic structural units linking to each other via with corner-sharing, edge-sharing, face-sharing bond. At low pressure, the basic structural units are mainly linked via one bridge oxygen (the corner sharing bonds). As pressure increases, the fraction of edge sharing bonds (two bridge oxygen) increases meanwhile the fraction of corner sharing bonds significantly decrease. There is a slight increase with the fraction of face- sharing bonds (three bridge oxygen). The Ge-O bond distance is almost not dependent on pressure, meanwhile the Ge-Ge and O-O bond distances are significantly dependent on pressure. Under compression, the average coordination number of Ge tends to increase from fourfold (at ambient pressure) to six-fold (at high pressure). Moreover, structure of GeO2 glass has two-domain near 15 and 25 GPa. And at ambient pressure or high pressures, the struture of GeO2 glass has single domain. The dependence of the distribution of free volumes on pressure in GeO2 glass has been examined. The distribution of void radius has the Gaussian form and the position of the peak tend to shift to the left under compression.

Quantifying short-range order using atom probe tomography

Medium- and high-entropy alloys are an emerging class of materials that can exhibit outstanding combinations of strength and ductility for engineering applications. Computational simulations have suggested the presence of short-range order (SRO) in these alloys, and recent experimental evidence is also beginning to emerge. Unfortunately, the difficulty in quantifying the SRO under different heat treatment conditions has generated much debate on the atomic preferencing and implications of SRO on mechanical properties. Here we develop an approach to measure SRO using atom probe tomography. This method balances the limitations of atom probe tomography with the threshold values of SRO to map the regimes where the required atomistic neighbourhood information is preserved and where it is not. We demonstrate the method with a case study of the CoCrNi alloy and use this to monitor SRO changes induced by heat treatments. These species-specific SRO measurements enable the generation of computational simulations of atomic neighbourhood models that are equivalent to the experiment and can contribute to the further understanding and design of medium- and high-entropy alloys and other materials systems where SRO may occur.

Short-range ordering mechanics in FCC materials

Short-range order (SRO) has a crucial impact on the mechanical strength of metallic alloys. Recent atomistic investigations defined an average SRO and attempted to correlate it with the yield strength. We propose that the local change in SRO upon slip advance must dictate the strengthening, and we elaborate the methodology to establish the “SRO change” on a slip plane considering the Wigner-Seitz cell. The model captures the variation of lattice resistance (Critical Resolved Shear Stress; CRSS) in the crystal as the SRO changes depending on the probability of neighboring atoms. The methodology was applied to Ni-V binary alloys for a wide range of compositions and stacking fault widths. Dislocation core widths were determined as a function of SRO and energy parameters (unstable and intrinsic stacking fault energies; γus, γisf). The complex variation of CRSS with compositional variations shows good agreement with limited experimental results. The compositions corresponding to the transition from partial to full dislocations at higher vanadium contents are found depending on the SRO and the intrinsic energy levels.

Comparison of structures and properties of gels formed by corn starch with fresh or dried Mesona chinensis polysaccharide

Starch is a major dietary carbohydrate, but its digestion properties need to be improved. Mesona chinensis polysaccharides (MCPs) had a unique function in improving the flocculation performance of starch. This study investigated the effects of adding Mesona chinensis polysaccharide extracted from wet fresh and dry plants with one-year storage, namely WMCP and DMCP, on the physicochemical properties and digestion kinetics of corn starch(CS). The composition analysis showed both WMCP and DMCP were an acidic heteropolysaccharide rich in galacturonic acid and galactose, whereas showed different average main fraction molecular weights (Mw) of 47.36 kDa and 42.98 kDa, respectively. In addition, WMCP showed higher yield, purity and better physicochemical properties to CS than DWCP. Thermal analysis showed WMCP decreased more gelatinization temperatures and enthalpy of CS, and increased more freeze-thaw stability, water holding capacity, and textural parameters of CS gels than DMCP. Structural analysis revealed WMCP induced more changes in crystallinity, short-range order, and microstructure of CS, which inhibited retrogradation than DMCP. In vitro digestion assays demonstrated WMCP addition significantly increased higher resistant starch content by altering starch-starch and starch-MCP interactions than DWCP. Overall, MCPs addition beneficially modulated CS properties and digestion kinetics, providing a novel way to improve starch functionalities. Moreover, WMCP had more advantages to be chosen to form hydrocolloid with CS than DMCP.

Physicochemical properties of ultrasound-pretreated pea starch and its inclusion complexes with lauric acid

Ultrasound is a promising green technology for modifying starch. The influence of ultrasound pretreatment (UPT) at diverse temperatures on the morphology and molecular structure of pea starch and its ability to form inclusion complexes with lipids were investigated. After UPT at each temperature, the starch granules retained an unchanged crystalline structure but exhibited notable changes in short-range molecular order and molecular structure. In comparison with the samples treated at 0 and 20 °C, pea starch subjected to UPT at 40 °C had a significantly (P ≤ 0.05) higher complexing index with lauric acid (LA) and the starch-LA inclusion complex exhibited a higher enthalpy change, relative crystallinity, and resistant starch content. These differences were attributed to the higher temperature causing changes in the disruption points of starch chains and an enlargement in the molecular weight of linear chains. These results may promote the utilization of ultrasound for effective starch modification.

Local structure, thermodynamics, and melting of boron phosphide at high pressures by deep learning-driven abinitio simulations.

Boron phosphide (BP) is a (super)hard semiconductor constituted of light elements, which is promising for high demand applications at extreme conditions. The behavior of BP at high temperatures and pressures is of special interest but is also poorly understood because both experimental and conventional abinitio methods are restricted to studying refractory covalent materials. The use of machine learning interatomic potentials is a revolutionary trend that gives a unique opportunity for high-temperature study of materials with abinitio accuracy. We develop a deep machine learning potential (DP) for accurate atomistic simulations of the solid and liquid phases of BP as well as their transformations near the melting line. Our DP provides quantitative agreement with experimental and abinitio molecular dynamics data for structural and dynamic properties. DP-based simulations reveal that at ambient pressure, a tetrahedrally bonded cubic BP crystal melts into an open structure consisting of two interpenetrating sub-networks of boron and phosphorous with different structures. Structure transformations of BP melt under compressing are reflected by the evolution of low-pressure tetrahedral coordination to high-pressure octahedral coordination. The main contributions to structural changes at low pressures are made by the evolution of medium-range order in the B-subnetwork and, at high pressures, by the change of short-range order in the P-subnetwork. Such transformations exhibit an anomalous behavior of structural characteristics in the range of 12-15GPa. DP-based simulations reveal that the Tm(P) curve develops a maximum at P ≈ 13 GPa, whereas experimental studies provide two separate branches of the melting curve, which demonstrate the opposite behavior. Analysis of the results obtained raises open issues in developing machine learning potentials for covalent materials and stimulates further experimental and theoretical studies of melting behavior in BP.

Structure formation processes in fullerene mixtures

Glass formation processes in condensed matter are characterized by some specific short-range order changes in the arrangement of particles (atoms/molecules/ions). So, the short-range structural order in supercooled liquids and glasses is characterized by fivefold symmetry in the arrangement of particles, often referred to as icosahedral (ideal or distorted) short-range order. This article is devoted to the study of local structural features of the supercooled melt of the A20B80 fullerene mixture (where A = C60 and B = C70) obtained under various cooling protocols in order to elucidate the mechanism of formation of the icosahedral short-range order in binary molecular liquids. Comprehensive studies of the properties of a fullerene mixture melt were carried out using large-scale molecular dynamics simulations followed by structural and cluster analysis. The crystallization temperature and the critical glass transition temperature of the system were calculated to be T_m~1439 K and T_c~1238 K, respectively. It has been established that the crystallization of a binary fullerene mixture proceeds according to the polycrystalline scenario with the formation of clusters with fcc and hcp symmetries. It is shown that in a supercooled fullerene mixture, the short-range icosahedral order is formed by an insignificant number of ideal icosahedral clusters and a certain set of distorted icosahedral clusters, the fraction of which remains practically unchanged at temperatures below the critical glass transition temperature. Keywords: molecular dynamics, fullerenes, short-range order, structural ordering.

Процессы структурообразования в фуллереновых смесях

Glass formation processes in condensed matter are characterized by some specific short-range order changes in the arrangement of particles (atoms/molecules/ions). So, the short-range structural order in supercooled liquids and glasses is characterized by fivefold symmetry in the arrangement of particles, often referred to as icosahedral (ideal or distorted) short-range order. This article is devoted to the study of local structural features of the supercooled melt of the A20B80 fullerene mixture (where A = C60 and B = C70) obtained under various cooling protocols in order to elucidate the mechanism of formation of the icosahedral short-range order in binary molecular liquids. Comprehensive studies of the properties of a fullerene mixture melt were carried out using large-scale molecular dynamics simulations followed by structural and cluster analysis. The crystallization temperature and the critical glass transition temperature of the system were calculated to be Tm ≈ 1439 K and Tc ≈ 1238 K, respectively. It has been established that the crystallization of a binary fullerene mixture proceeds according to the polycrystalline scenario with the formation of clusters with fcc and hcp symmetries. It is shown that in a supercooled fullerene mixture, the short-range icosahedral order is formed by an insignificant number of ideal icosahedral clusters and a certain set of distorted icosahedral clusters, the fraction of which remains practically unchanged at temperatures below the critical glass transition temperature.

Effect of heat-moisture treatment (HMT) on thermal stability of starch gel and the surface adhesiveness of vermicelli

The molecular structure has an important influence on the surface adhesion of starch gel. In the present study, the surface adhesiveness of vermicelli after cooking was reduced by heat-moisture treatment (HMT), and the mechanism underlying the increased thermal stability was explored by measuring the changes in short-range order, crystallinity, the thickness of the crystalline layer, and the length of the double helix in the dry starch gel. The surface adhesiveness decreased by 72.12 % when the moisture content was 26 %. HMT increased the crystallinity, and the thickness of the crystalline layer of the starch gel increased from 14.61 nm to 14.83–17.30 nm at 20–26 % moisture content. The molecular rearrangement and destruction of unstable short double helixes increased the proportion of long double helixes, resulting in an increased crystallinity and layer thickness.

Effect of High Hydrostatic Pressure Processing on Starch Properties of Cassava Flour

The aim of this study was to utilize high-pressure processing (HPP) to modify cassava flour through altering the starch components. Specifically, the effect of HPP processing variables, i.e., pressure (0.10 or untreated, 300, 400, 500, and 600 MPa), flour concentration (FC; 10, 20, and 30%), and holding time (HT; 10 and 30 min) on starch-related properties was studied. Microstructural integrity, thermal properties, and starch susceptibility to digestive enzymes were determined. A three-way ANOVA was performed to identify the interaction effect between these process variables. In general, 600 MPa consistently transformed the crystalline starch into an amorphous one. HPP-induced gelatinization led to enlarged starches with loss of birefringence, reduced relative crystallinity percentage, and changes in short-range order. The three-way interaction between the process variables was evident in the significant progressive rise in onset gelatinization temperature and degree of gelatinization, and the decline in gelatinization enthalpy from 500 to 600 MPa with decreasing FC and increasing HT. These changes caused an increased percentage of rapidly digestible starch and decreased resistant starch fraction. Overall, this study’s results imply the possibility of using HPP to modify the starch component in cassava flour and potentially create flours with varying levels of functionalities.

Pressure-induced local structural crossover in a high-entropy metallic glass

Achieving effective tuning of glass structures between distinct states is intriguing for fundamental studies and applications, but has previously turned out to be challenging in practice. High-entropy metallic glasses (HEMGs), as an emerging type of metallic glasses (MGs) based on the high-entropy effect, are expected to have more disordered and frustrated chemical short-range structure compared with conventional MGs. Therefore, HEMGs may offer possibilities for structure and properties tuning in glasses. In this work, we employ pressure as a tuning parameter and monitor the atomic structural evolution of a senary HEMG, ${\mathrm{Ti}}_{16.7}{\mathrm{Zr}}_{16.7}{\mathrm{Hf}}_{16.7}{\mathrm{Cu}}_{16.7}{\mathrm{Ni}}_{16.7}{\mathrm{Be}}_{16.7}$, up to \ensuremath{\sim}40 GPa using in situ synchrotron x-ray diffraction. Analysis of its structure factor in reciprocal space and reduced pair distribution function in real space both reveal a pressure-induced structural crossover at \ensuremath{\sim}20 GPa with a dramatic change in short-range order (SRO), while no similar phenomenon is observed in a conventional MG, ${\mathrm{Cu}}_{36}{\mathrm{Zr}}_{64}$, as a control sample, suggesting the pressure-induced highly tunable SRO in HEMGs originates from the local chemical complexity, namely, the high-entropy effect. These results confirm that enhanced flexibility and tunability of atomic structures could be achieved by introducing the high-entropy effect into MGs. Therefore, configurational entropy could be another dimension for exploring MGs with highly tunable structures and properties for various potential applications.

The deformation of short-range order leading to rearrangement of topological network structure in zeolitic imidazolate framework glasses

SummaryIn recent years, the study of the glassy structure of zeolitic imidazolate frameworks (ZIFs) has been a key breakthrough in glass science. Yet the theoretical understanding of the structure of these complex materials is still in its infancy, especially the short-range structure. The short-structural disorder of two ZIFs and their corresponding molten structure, namely, ZIF-4 and ZIF-62 are studied, using ab initio simulations. Changes in short-range order are investigated, particularly the changes in bond length, bond angle, and tetrahedral unit volume. Furthermore, the asymmetric distribution of organic groups caused by the benzimidazole functional group leads to the difference in short-range disorder between ZIF-4 and ZIF-62 glasses, which contribute to the glass-forming ability difference.

Structural, vibrational and magnetic properties of high-temperature (Ca4Nb2)1-xNd2xO9-6x solid solution

The sub-solidus phase relation in the Ca4Nb2O9–Nd2O3 pseudo-binary system has been examined by X-ray powder diffraction (XRD), thermal analysis (DSC/TGA), IR, Raman and EPR spectroscopy. The results have shown that a limited solid solution of Nd2O3 in Ca4Nb2O9 with (Ca4Nb2)1-xNd2xO9-6x (0≤ x ​≤ ​0.5) formula and monoclinic structure of H–Ca4Nb2O9 is formed. The cell parameters of the solid solution linearly increase with increasing Nd2O3 content which is in accordance with the Vegard's law. The composition evolution of selected IR and Raman bands confirmed a change in short-range order for investigated ceramic solid solution. Temperature dependence of magnetic susceptibility and Curie-Weiss temperature for new solid solution were analyzed.

Shear Softening in a Metallic Glass: First-Principles Local-Stress Analysis.

Metallic glasses deform elastically under stress. However, the atomic-level origin of elastic properties of metallic glasses remain unclear. In this Letter using abinitio molecular dynamics simulations of the Cu_{50}Zr_{50} metallic glass under shear strain, we show that the heterogeneous stress relaxation results in the increased charge transfer from Zr to Cu atoms, enhancing the softening of the shear modulus. Changes in compositional short-range order and atomic position shifts due to the nonaffine deformation are discussed. It is shown that the Zr subsystem exhibits a stiff behavior, whereas the displacements of Cu atoms from their initial positions, induced by the strain, provide the stress drop and softening.

Structure and optical properties of the photosensitive hybrid Ti-contained polymer materials for photonics

Titanium-containing interpenetrating polymer networks (Ti-IPNs) based on the cross-linked polyurethane, poly (hydroxyethyl methacrylate) and poly (titanium oxide) have been synthesized. First poly (titanium oxide) was synthesized by sol-gel method in the presence of 2-hydroxyethyl methacrylate at different molar ratio of Ti (OPri)4/H2O. The results obtained by method of optical spectrophotometry shows that the light transmission coefficients (T, %) of titanium-containing interpenetrating polymer networks samples was 90.7–91.0% at λ = 650 nm. According to EPR data, UV irradiation in the air at room temperature of Ti-IPN samples is accompanied by appearance of signal of paramagnetic centers with broad isotropic signal at g1 = 2.010 and also noticeably splitted signal at g2 = 2.003 and g3 = 1.967. First and second of them can be ascribed to the oxygen-containing “hole scavenger”, while the third one is associated with the Ti3+ paramagnetic ions. The low rate of the electron–hole pair recombination at room temperature in the air demonstrates efficient separation of the charged particles in the hybrid material. X-ray diffraction analysis indicates that Ti-IPN sample have an amorphous structure. UV-induced charge separation and subsequent charge recombination in Ti-IPNs cause the changes in short-range order in the arrangement of polymer macrochains.

Transformation of hydrogen bond network during CO2 clathrate hydrate dissociation

The kinetic process of the solid-liquid first-order phase transition of carbon dioxide CS-I hydrates with various cavity occupation ratios has been investigated in order to understand the framework of the H-bond network and the local structure of each water molecule. This includes the time dependent change in short-range order at temperatures close to the melting point and comparison with the hexagonal ice structure. Using the molecular dynamics method, dependencies of the internal energy of the studied systems on the time of heating were found. Jumps in the internal energy of solids in the range at 275–300K indicate a phase transition. The study of the oxygen‑oxygen radial distribution and hydrogen‑oxygen‑oxygen mutual orientation angles between molecules detached at no >3.2Å led to the determination of the H-bond coordination number for all molecules and the total number of H-bonds and showed instantaneous (<1ns) reorganization of the short-range order of all molecules. Structural analysis of neighbor water molecule pairs showed ~10–15% decrease in the H-bond number after melting whereas all molecules form a single long-range H-bond network. Analysis of the H-bond network showed minor changes in the H-bond interaction energy at the solid-liquid phase transition.

Solubility investigations in the amorphous calcium magnesium carbonate system.

Amorphous precursors are known to occur in the early stages of carbonate mineral formation in both biotic and abiotic environments. Although the Mg content of amorphous calcium magnesium carbonate (ACMC) is a crucial factor for its temporal stabilization, to date little is known about its control on ACMC solubility. Therefore, amorphous Ca x Mg1-x CO3·nH2O solids with 0 ≤ x ≤ 1 and 0.4 ≤ n ≤ 0.8 were synthesized and dispersed in MgCl2-NaHCO3 buffered solutions at 24.5 ± 0.5 °C. The chemical evolution of the solution and the precipitate clearly shows an instantaneous exchange of ions between ACMC and aqueous solution. The obtained ion activity product for ACMC (IAPACMC = "solubility product") increases as a function of its Mg content ([Mg]ACMC = (1 - x) × 100 in mol%) according to the expression: log(IAPACMC) = 0.0174 (±0.0013) × [Mg]ACMC - 6.278 (±0.046) (R 2 = 0.98), where the log(IAPACMC) shift from Ca (-6.28 ± 0.05) to Mg (-4.54 ± 0.16) ACMC endmember, can be explained by the increasing water content and changes in short-range order, as Ca is substituted by Mg in the ACMC structure. The results of this study shed light on the factors controlling ACMC solubility and its temporal stability in aqueous solutions.

Structural and thermodynamic mixing properties of [formula omitted] monazite-type solid solutions

La1−xNdxPO4 monazite-type ceramics were synthesized by precipitation and sintering. The obtained crystalline powders and pellets were structurally characterized by X-ray diffraction, electron microscopy, and infrared and Raman spectroscopy. The determined unit cell constants agree with published values for the pure end-members ranging from LaPO4 to DyPO4, as well as with values for known mixed monazite-type lanthanide orthophosphates, indicating a homogeneous solid solution. However, Raman spectroscopy shows a change in short-range order and the results of high temperature oxide melt solution calorimetry suggest a subregular solid solution, which requires two Margules parameters to calculate the observed enthalpy of mixing ΔHmix for La1−xNdxPO4, which is positive and asymmetric and shows a maximum at x = 0.299 (ΔHmix=7.53±0.01kJmol−1) at 298 K.

Properties of (TiZrNbCu)1-xNix metallic glasses

Recent studies (J. Alloys Compd. 695 (2017) 2661) of the electronic structure and properties of (TiZrNbCu)1-xNix (x ≤ 0.25) amorphous high entropy alloys (a-HEA) have been extended to x = 0.5 in order to compare behaviours of a-HEA and conventional Ni-base metallic glasses (MG). The amorphous state of all samples was verified by thermal analysis and X-ray diffraction (XRD). XRD indicated a probable change in local atomic arrangements, i.e. short-range-order (SRO) for x ≥ 0.35. Simultaneously, thermal parameters, such as the first crystallization temperature Tx and the liquidus temperature showed a tendency to saturate for x ≥ 0.35. The same tendency also appeared in the magnetic susceptibility χexp and the linear term in the low temperature specific heat γ. The Debye temperatures and Young's moduli also tend to saturate for x ≥ 0.35. These unusual changes in SRO and all properties within the amorphous phase seem correlated with the change of valence electron number (VEC) on increasing x.

Vibrational entropy of disorder in Cu3Au with different degrees of short-range order.

L12 ordered Cu3Au and fcc-disordered samples with different degrees of short-range order were synthesised by annealing and/or quenching experiments. Low-temperature heat capacities were determined by relaxation calorimetry. From these data the vibrational entropy of disorder was derived. The calorimetric results show that the vibrational entropy does not depend on the degree of short-range order. The calorimetric investigations were complemented by density functional calculations with different functionals simulating various atomic configurations by super cells of different size. Using super cells containing 32 atoms, the computed entropies show only small variations with the change of short-range order in good agreement with the calorimetric results. Using, however, super cells with only 8 atoms, the results depend strongly on the chosen atomic configuration at variance with the calorimetric data. This result is important for investigating substances with larger molecules (e.g., silicate solid solutions) because such investigations are typically limited on super cells containing only a few sites on which substitution takes place.