Intermediate-range Structure Research Articles

Atomic-Scale Insights into the Effects of the Foaming Degree on the Glass-Ceramic Matrix Derived from Waste Glass and Incineration Bottom Ash.

Precise management of the inverse correlation between the total porosity and compressive strength is crucial for the progress of foaming glass-ceramics (FGCs). To deeply understand this relationship, we investigated the atomic-level transformations of five CO2-foaming FGC samples using molecular dynamics simulation. The short-range and intermediate-range structures of the FGCs with varying total porosities (36.68%, 66.28%, 66.96%, 72.21%, and 79.88%) in the system were elucidated. Na cations were observed to exhibit a strong interaction with CO2, accumulating at the surface of the pore wall and influencing the oxygen species. Therefore, the change in the atomic structure of the matrix was accompanied by an increase in the total porosity with an increasing CO2 content. Specifically, as the total porosity increased, the bridging oxygen content within the FGCs rose accordingly. However, once the total porosity exceeded 66.96%, the bridging oxygen content began to decline. This observation was significant considering the role of the bridging oxygen content in forming a continuous cross-linked network of chemical bonds, which contributed to the enhanced mechanical strength. Consequently, the influence of the total porosity on the oxygen species resulted in a two-stage reduction in the compressive strength. This study offers valuable insights for the development of high-strength lightweight FGCs.

The basic intermediate-range order structures in the FLiNaK–LaF3–Li2O melt: identification and characterisation

ABSTRACT In this paper, we investigate the structure of FLiNaK–LaF3 melt with small addition of Li2O through the theoretical approach combining ab initio molecular dynamics and simulation of the isolated structural units. The structure of the melt was studied in detail by calculation of radial distribution functions along with coordination numbers and radii. We found that oxyfluoride intermediate-range structure is formed in the melt. Our observations support the suggestions of other authors on formation of intermediate-range structures in fluoride melts containing metal oxides. Given structure shows long lifetime, the consideration of the isolated specie is valuable. We performed a simulation of ‘gas-phase’ [O2La4Fn] structure in order to calculate its Raman spectrum. It was found that the spectrum of the isolated structure agree in semi-quantitative manner with the vibrational density of states of the oxygen ions in the melt.

Local- and Intermediate-range Partial Structure Study of As–Se Glasses

Local- and Intermediate-range Partial Structure Study of As–Se Glasses

Application of topological constraint theory to alkali borate and silicate glass systems

Principles of Topological Constraint Theory (TCT) were applied to alkali borate and silicate glass systems using intermediate range structural models over wide compositional ranges. The structural model for lithium borate was derived from the Feller, Dell, and Bray model [1] and extended to the terminal composition at R=3 where R is the molar ratio of lithium oxide to borate. The sodium borate structural model was built using both NMR [2] and Raman [3] data, and also included carbonate retention in the glass [4]. This model was extended to R=3 similarly to the lithium borate system. The silicate system models were created from 29Si NMR data [5] and also incorporated carbonate retention where necessary [6].Constraint models considered the effect of intermediate range structures on the system, and also incorporated the effect of “loose” alkali which is not directly associated with a non-bridging oxygen. Constraint models of the alkali borate, silicate, and borosilicate systems were then used to predict properties such as glass transition temperature and fragility.

Synthesis, Structure, and Photophysical Properties of Platinum Compounds with Thiophene-Derived Cyclohexyl Diimine Ligands.

Platinum(II) and platinum(IV) compounds were prepared by the stereoselective and regioselective reactions of thiophene-derived cyclohexyl diimine C^N^N-ligands with [Pt2Me4(μ-SMe2)2]. Newly synthesized ligands were characterized by NMR spectroscopy and elemental analysis, and Pt(II)/Pt(IV) compounds were characterized by NMR spectroscopy, elemental analysis, high-resolution mass spectrometry, and single-crystal X-ray diffraction. UV-vis absorbance and photoluminescence measurements were performed on newly synthesized complexes, as well as structurally related Pt(II)/Pt(IV) compounds with benzene-derived cyclohexyl diimine ligands, in dichloromethane solution, as solids, and as 5% by weight PMMA-doped films. DFT and TD-DFT calculations were performed, and the results were compared with the observed spectroscopic properties of the newly synthesized complexes. X-ray total scattering measurements and real space pair distribution function analysis were performed on the synthesized complexes to examine the local- and intermediate-range atomic structures of the emissive solid states.

Large-scale Molecular-dynamics Simulations of SiO2 Melt under High Pressure with Robust Machine-learning Interatomic Potentials

We have carried out molecular-dynamics simulations of SiO2 melt at 60 GPa in a system of about 30,000 atoms, with robust machine-learning interatomic potentials based on ab initio calculations. The large-scale simulations not only reproduced the ab initio calculations, but were also found to significantly improve the precision of the intermediate-range structure. Interatomic potentials determined using machine learning easily destabilize simulations of highly covalent melts under high pressure in an extended system with over one order of magnitude more atoms than those in the initial calculations used for data generation. The combination of potential averaging and active learning can efficiently suppress computational instability.

Temperature-induced densification in compressed basaltic glass revealed by in-situ ultrasonic measurements

Abstract Acoustic velocities of a model basalt glass (64 mol% CaMgSi2O6 + 36 mol% CaAl2Si2O8) were measured along different pressure-temperature (P-T) paths. One set of experiments involved isothermal compression-decompression cycles, performed at temperatures of 300, 641, 823, and 1006 K and pressures up to 12.2 GPa. The other set of experiments involved constant-load heating-cooling cycles at temperatures up to 823 K and pressures up to 7.5 GPa. Both sets of experiments were performed in a multi-anvil apparatus using a synchrotron-based ultrasonic technique. Our results show that the glass compressed isothermally at 300 K (cold-compression) displays anomalously decreasing compressional (VP) and shear (VS) wave velocities with increasing pressure until ~8 GPa. Beyond 8 GPa, both VP and VS start to increase sharply with pressure and irreversible densification of the glass occurred, producing large hysteresis loops of velocities upon decompression. However, for the glass compressed isothermally at increasingly higher temperatures (hot-compression), the velocity minima gradually shift to lower pressures. At temperature close to the glass transition temperature Tg, the velocity minima disappear completely, displaying a monotonic increase of velocities during compression and higher VP and VS during decompression. In addition, constant-load heating-cooling experiments show that velocities generally decrease slightly with increasing temperature, but start to increase once heated above a threshold temperature (~650 K). During cooling the velocities increase almost linearly with decreasing temperature, resulting in higher velocities (~1.5–2.5% higher) when returned to 300 K. This implies that a temperature-induced densification may have occurred in the glass at high pressures. Raman spectra on recovered samples show that the hot-compressed and high-P heated glasses contain distinctly densified and depolymerized structural signatures compared to the initial glass and the cold-compressed glass below the velocity transition pressure PT (~8 GPa). Such densification may be attributed to the breaking of bridging oxygen bonds and compaction in the intermediate-range structure. Our results demonstrate that temperature can facilitate glass densification at high pressures and point out the importance of P-T history in understanding the elastic properties of silicate glasses. Comparison with melt velocity suggests that hot-compressed glasses may better resemble the pressure dependence of velocity of silicate melts than cold-compressed glasses, but still show significantly higher velocities than melts. If the abnormal acoustic behaviors of cold-compressed glasses were used to constrain melt fractions in the mantle low-velocity regions, the melt fractions needed to explain a given velocity reduction would be significantly underestimated at high pressures.

Effect of sulphate ions on the physical and optical properties of zinc phosphate glasses containing Sm3+ ions

Lithium based zinc-phosphate containing Sm2O3 glasses of the system (5-x) Li2SO4 − 20Li2O − 45P2O5 − 30ZnO - xSm2O3, (where x = 0, 0.1, 0.5, 1, 2 and 3 mol%) were prepared by melt quenching technique. The amorphous nature of the prepared glasses is ascertained by X-ray diffraction. The density and molar volume are found to vary non-linearly with Sm2O3 content. The addition of modifier oxides such as Li2O to P2O5 glass would break P-O-P bonds and resulting in the creation of non-bridging oxygen’s. The creation of non-bridging oxygen atoms makes the structure less rigid and would leads to the formation of weaker phosphate structural entities. This would lead to the formation of voids between the phosphate groups. The addition of alkali and samarium content in the phosphate glasses is accountable for the collective number of the non– bonded oxygens and this may cause a non-linear variation in the volume of the network structure which in turn lead to non-linear variation in the density. The optical spectrum consists of a characteristic Ultraviolet absorption bands of Sm3+ ions in the range 200–400 nm and other strong bands at 940 nm and 1100 nm which are considered to originate from the transitions of ground state to the different excited states. The optical band gap energies were determined from both ultraviolet band edges and Tauc’s plots. The band gap energy varies non-linearly with Sm2O3 content. The non-linear variation in density, molar volume and band gap energy discloses the intermediate-range structure composed of PO4and ZnO4tetrahedra and are discussed in view of the polymeric chain of phosphate network structure.

Complete Description of the LaCl3-NaCl Melt Structure and the Concept of a Spacer Salt That Causes Structural Heterogeneity.

Lanthanides are important fission products in molten salt reactors, and understanding their structure and that of their mixtures is relevant to many scientific and technological problems including the recovery and separation of rare earth elements using molten salt electrolysis. The literature on molten salts and specifically on LaCl3 and LaCl3-NaCl mixtures is often fragmented, with different experiments and simulations coinciding in their explanation for certain structural results but contradicting or questioning for others. Given the very practical importance that actinide and lanthanide salts have for energy applications, it is imperative to arrive at a clear unified picture of their local and intermediate-range structure in the neat molten state and when mixed with other salts. This article aims to unequivocally answer a set of specific questions: is it correct to think of long-lived octahedral coordination structures for La3+? What is the nature as a function of temperature of networks and intermediate-range order particularly upon dilution of the trivalent ion salt? Is the so-called scattering first sharp diffraction peak (FSDP) for neat LaCl3 truly indicative of intermediate-range order? If so, why is there a new lower-q peak when mixed with NaCl? Are X-ray scattering and Raman spectroscopy results fully consistent and easily described by simulation results? We will show that answers to these questions require that we abandon the idea of a most prominent coordination state for M3+ ions and instead think of multiple competing coordination states in exchange due to significant thermal energy in the molten state.

Coupling between Translational Diffusion of a Solute and Dynamics of the Heterogeneous Structure: Higher Alcohols and Ionic Liquids.

Translational diffusion of nonpolar monoatomic solutes in a room-temperature ionic liquid and 1-octanol was studied by molecular dynamics simulation. The diffusion coefficient was evaluated in two different ways: (1) from the mean-square displacement of a freely diffusing solute and (2) from the time correlation function of force acting on a fixed solute. The diffusion of the free solute is much greater than the prediction of the Stokes-Einstein (SE) relation when the size of the solute is small, as has been reported by many experimental works. In contrast, the friction on fixed small solutes follows the SE relation. The mechanism of the solute diffusion in both solvents was then analyzed based on the coupling between the translational motion of the solute and the collective dynamics of the heterogeneous intermediate-range structure characteristic to these solvents. Analysis revealed that the coupling is present in all systems, but the relaxation is fast in the cases of free and small solutes. This suggests that the coupling can relax through the motion of the solute when the solute is free and small, while the relaxation of the heterogeneous structure itself is required for large or fixed solutes. The difference in the relaxation dynamics of the friction on the solute and the shear viscosity is explained as the coupling with different dynamic modes of the solvent. Therefore, the validity of the SE relation may not be a good criterion to judge whether the mechanisms of the diffusion and the viscosity are the same or not.

Short- to Intermediate-Range Structure, Transport, and Thermophysical Properties of LiF–NaF–ZrF4 Molten Salts

LiF–NaF–ZrF4 multicomponent molten salts are identified as promising candidates for coolant salts in molten salt reactors and advanced high-temperature reactors. This study focused on low-melting point salt compositions of interest: 38LiF–51NaF–11ZrF4, 42LiF–29NaF–29ZrF4, and 26LiF–37NaF–37ZrF4. Ab-initio molecular dynamics (AIMD) calculations were performed and compared with available experimental data to assess the ability of rigid ion models (RIM) to reproduce short- to intermediate-range structure, transport, and thermophysical properties of the LiF–NaF–ZrF4 salt mixtures. It is found that as ZrF4 mol% increases, the average cation–anion coordination number (CN) of monovalent cations (Li+, Na+) obtained from RIM calculations decreases, while multivalent Zr4+ CN varied from 15% to 19% in comparison to corresponding AIMD values. In addition, RIM is found to predict the existence of 7, 8, and 9 coordinated fluorozirconate complexes, while AIMD and the available experimental data showed an occurrence of 6, 7, and 8 coordinated complexes in the melt. The intermediate-range structure analysis revealed that while the RIM parameters are able to reproduce a local structure for lower ZrF4 mol% salts such as in 38LiF–51NaF–11ZrF4, an extensive fluorozirconate network formation is observed in RIM simulations for higher ZrF4 mol% compositions. The network generated by RIM parameters is found to be mainly connected by “corner-sharing” fluorozirconate complexes as opposed to both “edge-sharing” and “corner-sharing” connectively portrayed by AIMD. It is found that a close agreement between AIMD and the RIM salt structure for the 11-mol% ZrF4 salt resulted in good agreement in the calculated Zr diffusivities and the viscosity values. However, due to the inaccurate short- to intermediate-range structure prediction by RIM for higher ZrF4 mol% compositions, thermophysical properties such as densities and heat capacity differ by up to 26% and 27%, respectively, upon comparison with AIMD and experimental values. Also, the network-dominated properties such as diffusion coefficients and viscosities differed by up to two and three orders of magnitude, respectively. This study signifies the importance of accurate salt structure generation for an accurate prediction of transport and thermophysical properties of multicomponent molten salts.

Elucidating the influence of structure and Ag+-Na+ ion-exchange on crack-resistance and ionic conductivity of Na3Al1.8Si1.65P1.8O12 glass electrolyte

Glasses are emerging as promising and efficient solid electrolytes for all-solid-state sodium-ion batteries. However, they still suffer from poor ionic conductivity and crack-resistance, which need to be improved for better battery performance, reliability, and service life. The current study shows a significant enhancement in crack resistance (from 11.3 N to 32.9 N) for Na3Al1.8Si1.65P1.8O12 glass (Ag-0 glass) upon Na+-Ag+ ion-exchange (IE) due to compressive stresses generated in the glass surface while the ionic conductivity values (∼10−5 S/cm at 473 K) were retained. In this study, magic angle spinning-nuclear magnetic resonance (MAS-NMR), molecular dynamics (MD) simulations, Vickers micro hardness, and impedance spectroscopic techniques were used to evaluate the intermediate-range structure, atomic structure, crack resistance and conductivity of the glass. MAS-NMR and MD simulations confirm the presence of Si‒O‒Al‒O‒P groups in the glass, thus enabling formation of Na percolated channel regions. AC-conductivity analysis for Ag-0 and ion-exchanged Ag-0 glass suggests that the mobility of Na+ ion increases with increasing temperature. It is observed that the measured mean square displacement (〈R2(tp)〉) for sodium cations using AC-conductivity isotherms is nearly constant up to 448 K and then increases with increasing temperature up to 523 K. From the impedance spectra for ion-exchanged Ag-0 glass, it is identified that the increase in 〈R2(tp)〉 and thereby, the mobility of sodium-ions for Ag-0 glass is due to the structural variations in the Ag-0 glass with increasing the temperature. Overall, the mechanisms presented in this article helps in formulating better glass based electrolyte materials for room temperature or high temperature sodium-ion batteries.

High-energy X-Ray diffraction study of multiwalled carbon nanotubes fabricated by arc discharge plasma process

Structural features of multiwalled carbon nanotubes (MWCNTs) have been analyzed quantitatively by high-energy X-ray diffraction (HE-XRD) with atomic pair distribution function (PDF) technique. It has been found that the nanotubes are mainly of scroll type and own an atomic arrangement defined on the nanometer length scale in terms of a unit cell and symmetry. They exhibit multipart local (sub-nanometer) and intermediate range (on nano-length-scale) structures. The structural information at different length-scales was used to probe the interlayer spacing distribution within the nanotubes. The radial dependence of interlayer spacing observed in pristine nanotubes presents tendency for alteration to uniform spacing of layer in the course of heating-cooling cycle in the range of 298–450 K. These spatial changes illustrate modification of Fermat type stroll with uneven interlayer distances in pristine nanotubes to more stable equidistant interlayer Archimedean spiral type in the heating-cooling treated ones.

Connecting Packing Efficiency of Binary Hard Sphere Systems to Their Intermediate Range Structure.

Using computed x-ray tomography we determine the three dimensional (3D) structure of binary hard sphere mixtures as a function of composition and size ratio of the particles q. Using a recently introduced four-point correlation function we reveal that this 3D structure has on intermediate and large length scales a surprisingly regular order, the symmetry of which depends on q. The related structural correlation length has a minimum at the composition at which the packing fraction is highest. At this composition also the number of different local particle arrangements has a maximum, indicating that efficient packing of particles is associated with a structure that is locally maximally disordered.

A Simulation Study of the Amorphous Germania Structure up to 70 GPa

This work presents the effect of pressure on the local microstructure of amorphous Germania (GeO2). The Molecular Dynamics simulation was performed on systems at 900 K and high pressure up to 70 GPa. The structural properties have been analyzed through the pair correlation function, coordination number distribution, and structure factors. The structural phase transition process starts occurring at 30 GPa. At above 30 GPa, the degree of structural order increases and the intermediate-range order structure depends strongly on pressure. Correlation between the peaks in the plot of structure factor and the topology of basic structural units GeOn(n = 4-6) is also discussed in detail in this paper.

Laser-induced structural modification in calcium aluminosilicate glasses using molecular dynamic simulations

Glass structures of multicomponent oxide systems (CaO–Al2O3–SiO2) are studied using a simulated pulsed laser with molecular dynamics. The short- and intermediate-range order structures revealed a direct correlation between the transformation of Al(IV) to Al(V), regions of increased density following laser processing, inherent reduction in the average T–O–T (T = Al, Si) angle, and associated elongation of the T–O bonding distance. Variable laser pulse energies were simulated across calcium aluminosilicate glasses with high silica content (50–80%) to identify densification trends attributed to composition and laser energy. High-intensity pulsed laser effects on fictive temperature and shockwave promotion are discussed in detail for their role in glass densification. Laser-induced structural changes are found to be highly dependent on pulse energy and glass chemistry.

Detailed Investigations on Short- and Intermediate-Range Structures of Ge–Se Glasses near the Stiffness Transition Composition

In order to improve the reliability of short- and intermediate-range atomic structures of GexSe1−x glasses, high quality neutron diffraction data, in both the real and reciprocal spaces, were added...

High pressure effect on the short- and intermediate-range structure of depolymerized soda lime silicate glass: Insights from micro-Raman spectroscopy

The network structure pressure dependence of a modified soda lime silicate glass, containing CaF2 and lower SiO2 content, was investigated by micro-Raman spectroscopy. The glass structure was first analyzed under normal pressure conditions in terms of network depolymerization, by comparing with commercial soda lime glass. Using calculation of non-bridging oxygens per tetrahedron (NBO/T), it was found that while commercial soda lime glasses have Q4 and Q3 units, the studied glass system presents a depolymerized structure and it is composed, on average, of Qn with n = 3 and 2. Changes due to high hydrostatic pressure were evaluated by using a diamond anvil cell up to 19 GPa. Raman scattering was used to calculate Si–O–Si angular population according to the network central force, which showed a progressive angle closure with pressure. The Raman spectrum of recovered sample, after compression/decompression cycle, showed negligible changes, suggesting that initial amorphous phase of modified glass is highly stable. The glass showed very high incompressibility, compared to aluminates, silicates, lanthanum borogermanate, or even regular soda lime glasses, suggesting that its bulk modulus is relative high. Polymerized glasses have great space vacancies within the network structure, on the contrary it was observed that the studied glass presents a densely packed structure reflecting on high incompressibility, which decreased the magnitude of permanent densification.

Indentation-Induced Structural Changes in Vitreous Silica Probed by in-situ Small-Angle X-Ray Scattering

The transient (or permanent) structural modifications which occur during local deformation of oxide glasses are typically studied on the basis of short-range data, for example, obtained through vibrational spectroscopy. This is in contrast to macroscopic observations, where variations in material density can usually not be explained using next-neighbor correlations alone. Recent experiments employing low-frequency Raman spectroscopy have pointed-out this issue, emphasizing that the deformation behavior of glasses is mediated through structural heterogeneity and drawing an analogy to granular media. Here, we provide additional support to this understanding, using an alternative experimental method. Structural modification of vitreous silica in the stress field of a sharp diamond indenter tip was monitored by in-situ small-angle X-ray scattering. The influenced zone during loading and after unloading was compared, demonstrating that changes in the position of the first sharp diffraction peak (FSDP) directly in the center of the indent are of permanent character. On the other hand, variations in the amplitude of electron density fluctuations appear to fully recover after load release. The lateral extent of the modifications and their relaxation are related to the short- to intermediate-range structure and elastic heterogeneity pertinent to the glass network. With support from Finite Element Analysis, we suggest that different structural length scales govern shear and isotropic compaction in vitreous silica.

Intermediate range structure of amorphous Cu2GeTe3: ab initio molecular dynamics study

We have investigated the intermediate range structure of amorphous Cu2GeTe3 based on ab initio molecular dynamics simulations. The highest population of ring size is three, which makes the triangle structure. This ring consists of mainly Cu2Te. Rings may also consist of CuCuCu, Cu2Ge, and CuGeTe, where approximately 88% of Cu atoms in the system are related with the three-membered ring. The second highest population of ring size is five. Three- and five-membered rings in the amorphous phase originate from six-membered ring in the crystalline phase. This situation can enhance the phase transition between crystalline and amorphous phases. In the phase change process, Cu atoms may diffuse in the amorphous state with changing bonds. The diffusion coefficient of Cu DCu is estimated to be approximately 0.12 × 10−9 m2 s−1. Such high diffusion coefficient of Cu atoms is contributed from only 10% of Cu atoms in the amorphous phase.