Tetrahedral Network Research Articles

Comparing silicon mineral species of different crystallinity using Fourier transform infrared spectroscopy

In soils, various solid silica (Si) species exhibit different weathering behaviors and surface reactivities, which are among other characteristics related to the crystallinity of the silicate tetrahedral network. Amorphous species exhibit faster weathering and generally possess a larger specific surface area in comparison to crystalline species. However, the characterization of these different species is commonly based on wet chemical extraction methods, which lack selectivity. While Fourier transform infrared spectroscopy (FTIR) in the mid-infrared range can differentiate between short-range ordered aluminosilicates (SROAS) and pure amorphous silica (ASi), few systematic studies are found on the IR spectral features that distinguish solid Si species by crystallinity. This study aims to identify FTIR absorption bands that can differentiate Si species based on their crystallinity. Our data clearly indicate that ASi can be distinguished from very crystalline silica (quartz) and sea sand. The absorption band at approximately 800 cm−1 in the FTIR spectra allows determining the degree of crystallinity of the studied ASi species since the band becomes smaller and the band maximum shifted toward lower wavenumbers with increasing degree of crystallinity. Hence, FTIR spectra may be used to differentiate certain Si species in complex samples like soils, allowing the estimation of weatherability and surface reactivity of those species.

A novel Al-based MOF with straight channel and pocket pore structure for trace benzene adsorption and benzene/cyclohexane separation

Benzene (Bz) vapor poses significant health risks to humans, even at trace concentrations. Additionally, the separation and recycling of Bz and cyclohexane (Cy) is challenging due to their similar kinetic diameters and boiling points. Developing an adsorption-separation material with stronger interactions with Bz than with Cy could serve as a viable strategy for trace Bz adsorption and Bz/Cy separation. In this study, we present a novel aluminum-based metal–organic framework, ZJU-521(Al), composed of tetrakis (4-carboxyphenyl)methane and a helical chain [Al5(OH)7(−COO)8]∞, featuring a simple network of one-way rods and tetrahedra. This framework exhibited a uniform micropore size of 7.23 Å and a specific surface area of 1,248 m2 g−1, demonstrating excellent trace Bz adsorption (4.18 mmol g−1) at P/P0 = 0.01, attributed to its straight channel and orthogonal-array pocket pore structure. The ideal adsorbed solution theory selectivity and separation factor values of ZJU-521(Al) for Bz/Cy were 22.50 and 6.20, respectively, indicating its potential as a material for Bz/Cy separation. Multicomponent simulations showed that Bz molecules were preferentially adsorbed in the pocket due to stronger interactions, such as Al–π interactions. Thus, ZJU-521(Al) exhibits stronger interactions with Bz than with Cy, facilitating effective Bz/Cy separation.

X-ray diffraction and quasielastic neutron scattering studies of the structure and dynamic properties of water confined in ordered microporous carbon pores

The structure and dynamic properties of capillary-condensed water confined in ordered microporous carbon (OMC) of pores diameter 18.7 Å are investigated over a temperature range of 200–300 K by adsorption/desorption isotherms, X-ray diffraction (XRD), and quasielastic neutron scattering (QENS). The nitrogen adsorption/desorption isotherm of OMC pores at 77 K exhibits an I-type pattern. The water adsorption/desorption isotherm of OMC pores at 298 K is of type V. The XRD data on water confined in OMC reveal that the tetrahedral network structure of water is perturbed from the bulk water structure, but not to such an extent as found for water confined in MCM-41 and Ph-PMO previously reported. With decreasing the temperature, the ∼2.8 Å peak shifts to shorter distances, while the second-neighbor H2O– H2O interaction distances gradually increase from 3.95 Å and 4.49 Å to 4.43 Å and 4.84 Å, indicating a tendency to form a more tetrahedral-like hydrogen-bonded water structure at subzero temperatures. Below 230 K, the hexagonal ice Ih was partially formed in OMC pores. The QENS spectra were analyzed using a jump-diffusion model to translate water molecules. The translational diffusion of water molecules in OMC pores is comparable to that of bulk water at 300 K and higher than that in MCM-41, and the mobility slows as the temperature decreases. The elastic incoherent structure factor (EISF) analysis found evidence for immobile and mobile fractions of confined water. The mobile fraction exhibited jump diffusion, with a jump length consistent with a sphere of confinement radius of 4–8 Å. The results obtained in the present work are compared with those reported for MCM-41 with a hydrophilic interface and Ph-PMO with an amphiphilic interface, and the influence of interface effect on local structure and dynamic properties of confined water is discussed.

Generating interstitial water within the persisting tetrahedral H-bond network explains density increase upon compressing liquid water

Despite its ubiquitous nature, the atomic structure of water in its liquid state is still controversially debated. We use a combination of X-ray Raman scattering spectroscopy in conjunction with ab initio and path integral molecular dynamics simulations to study the local atomic and electronic structure of water under high pressure conditions. Systematically increasing fingerprints of non-hydrogen-bonded H[Formula: see text]O molecules in the first hydration shell are identified in the experimental and computational oxygen K-edge excitation spectra. This provides evidence for a compaction mechanism in terms of a continuous collapse of the second hydration shell with increasing pressure via generation of interstitial water within locally tetrahedral hydrogen-bonding environments.

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.

Effect of TiO2 on the structural properties and viscosity of CaO-SiO2-8.25 %MgO-15 %Al2O3-TiO2 slags

As a raw material for ironmaking, vanadium-bearing titanomagnetite will leads to an increase in the TiO2 content of blast-furnace slag and deteriorates the metallurgical properties of the slag. In this study, the effect of TiO2 content on the viscosity of CaO-SiO2–8.25 %MgO-15 %Al2O3-TiO2 slag system at fixed w(CaO)/w(SiO2) ratio of 1.2 was investigated, and Raman spectroscopy focusing on the relationship between the structure of high TiO2-bearing blast furnace slag and viscosity was performed. The findings showed that under the experimental condition, the viscosity of slag decreases with the increase of TiO2 content over a range of 20 to 35 %. The melting temperature of slag increases first and then decreases after w(TiO2) is higher than 30 %. The viscous-flow activation energy of slag decreases with the increase of TiO2 content, which has a concomitant variation corresponding with the results of the effect of TiO2 on viscosity. The analysis of Raman spectroscopy results reveals that the blast-furnace slag system is dominated by [SiO4]4- network structure. As the TiO2 content increases, more and more Ti4+ enters the silica-oxygen tetrahedral network structure, disrupting the Si-O-Si bond to form the [TiO4]4- structural unit and a small portion of the [TiO6]8- structural unit. The NBO/Si value of the Si4+ in the tetrahedron unit as an index for the degree of depolymerization of slags increased from 1.62 to 2.60 as the TiO2 content increased, the slag structure was gradually simplified and the slag viscosity was gradually decreased.

Study of the Structure of Zn and Na Borophosphate Glasses Using X-ray and Neutron Scattering Techniques

The atomic structures of Zn and Na borophosphate glasses were studied using X-ray and neutron scattering techniques. Peaks assigned to the B−O, P−O, and O−O distances confirm that only BO4 units co-exist with the PO4 tetrahedra. The Zn−O and Na−O coordination numbers are found to be a little larger than four. The narrowest peaks of the Zn−O first-neighbor distances exist for the glasses along a line connecting the Zn(PO3)2 and BPO4 compositions (50 mol% P2O5), which is explained by networks of ZnO4, BO4, and PO4 tetrahedra with twofold coordinated oxygens. The calculated amounts of available oxygen support this interpretation. Broadened peaks occur for glasses with lower P2O5 contents, which is consistent with the presence of threefold coordinated oxygens. The two distinct P−O peak components of the Zn and Na borophosphate glasses differ in their relative abundances. This is interpreted as follows: Na+ cations coordinate oxygens in some P−O−B bridges, which is something not seen for the Zn2+ ions.

Local Structure, Structural, Vibrational, and Optical Properties of Natural Zircon

Structural properties of Indian metamict single zircon crystals are studied by comparing their properties with those of synthetic zircon synthesized via solid‐state reaction method, which serves as the standard. X‐Ray diffraction (XRD) data reveal changes in lattice parameters and the presence of strain, metamictization, etc. It is found that the degree of crystallinity is ≈63.8% indicating the simultaneous presence of crystalline and disordered regions. These changes are likely due to the presence of several radioactive/nonradioactive elements. The presence of such elements is observed and the sample composition is analyzed through total reflection X‐Ray fluorescence. XRD crystallographic data are further utilized as input for analyzing X‐Ray absorption spectroscopy data recorded around Zr central absorbing atom. X‐Ray absorption near‐edge structure shows slight modification in the white line feature and some disorder compared to the synthetic one. Reduced coordination number observed from extended X‐Ray absorption fine structure suggests the presence of disorder in local structure. Micro‐Raman spectroscopy indicates that crystalline behavior varies across different locations, suggesting that the sample has undergone varying degrees of metamictization, confirming a nonuniform distribution of elements. The work documents and analyses structural evolution within isolated silica tetrahedron network in association of Zr4+ cation as a function of self‐irradiation and recovery over millions of years and correlating the same with optical properties.

Local number fluctuations in ordered and disordered phases of water across temperatures: Higher-order moments and degrees of tetrahedrality.

The isothermal compressibility (i.e., related to the asymptotic number variance) of equilibrium liquid water as a function of temperature is minimal under near-ambient conditions. This anomalous non-monotonic temperature dependence is due to a balance between thermal fluctuations and the formation of tetrahedral hydrogen-bond networks. Since tetrahedrality is a many-body property, it will also influence the higher-order moments of density fluctuations, including the skewness and kurtosis. To gain a more complete picture, we examine these higher-order moments that encapsulate many-body correlations using a recently developed, advanced platform for local density fluctuations. We study an extensive set of simulated phases of water across a range of temperatures (80-1600K) with various degrees of tetrahedrality, including ice phases, equilibrium liquid water, supercritical water, and disordered nonequilibrium quenches. We find clear signatures of tetrahedrality in the higher-order moments, including the skewness and excess kurtosis, which scale for all cases with the degree of tetrahedrality. More importantly, this scaling behavior leads to non-monotonic temperature dependencies in the higher-order moments for both equilibrium and non-equilibrium phases. Specifically, under near-ambient conditions, the higher-order moments vanish most rapidly for large length scales, and the distribution quickly converges to a Gaussian in our metric. However, under non-ambient conditions, higher-order moments vanish more slowly and hence become more relevant, especially for improving information-theoretic approximations of hydrophobic solubility. The temperature non-monotonicity that we observe in the full distribution across length scales could shed light on water's nested anomalies, i.e., reveal new links between structural, dynamic, and thermodynamic anomalies.

The water bimodal inherent structure and the liquid-liquid transition as proposed by the experimental density data.

The bulk water density data are studied in a very large temperature-pressure range, from stable liquid to glass in the frame of water polymorphism. Because this thermodynamic variable evidences a crossover T*, above which the hydrogen bond (HB) is unable to arrange tetrahedral networks, the T-dependence of their isobars was considered. Such an analysis also shows pressure, P*, around which their thermal behaviors are completely different: concave below P* (with maxima and minima) and convex above (without extremes). Having ρ's measured values of the bimodal structures of the liquid phase, HDL (ρHDL), made of not-bonded monomers (ρNHB) and partially bonded dimers plus trimers (ρNHB), and LDL tetramers (ρLDL) the isobars of the relative distributions [W(P, T)] of the three species (WLDL, WPHB, and WNHB) have been evaluated. The results were studied by means of a logistic function (LF) that details the evolutions of the relative polpulations of the water LDL and HDL phases by decreasing T (for the isobars, in the range of 0.1-400 MPa). The LFs analysis obtained by proposing a full connection between liquid water from its supercooled metastable phase to the stable up to the boiling temperature identifies the Widom line quite satisfactorily and fully supports the presence of the liquid-liquid critical point in the deep supercooled region, located at about 190K and in the range 200 > P > 180 MPa.

Weakening the silicate network through six-coordinated magnesium to achieve a high degree of crystallization of β-CaSiO3 in calcium borosilicate glass ceramics for 5G application

β-CaSiO3 with a low dielectric constant and low dielectric loss is one of the decisive components of commercial calcium borosilicate (CBS) low-temperature co-fired ceramic substrate. However, achieving a high degree of crystallization of β-CaSiO3 is difficult in CBS glass ceramics because of the competitive multiphase crystallization during sintering. We have shown that six-coordinated magnesium can be used to weaken the silicate network to achieve a high degree of crystallization of β-CaSiO3 in CBS glass ceramics. The appropriate MgO content to ensure a large amount of MgO6 production gradually destroys the [SiO4] tetrahedral network as the temperature increases, resulting in a β-CaSiO3 content of 76.2 vol%, when the MgO content is 2.71 mol%. The resulting material has the lowest dielectric constant (4.95@15 GHz) and dielectric loss (8 × 10−4@15 GHz), and the best three-point bend strength (77.43 MPa). Our work provides an effective method of changing the crystallization by modifying the glass network in silicate-based glass ceramics with a low dielectric constant.

Closed and open superconducting microwave waveguide networks as a model for quantum graphs.

We report on high-precision measurements that were performed with superconducting waveguide networks with the geometry of a tetrahedral and a honeycomb graph. They consist of junctions of valency three that connect straight rectangular waveguides of equal width but incommensurable lengths. The experiments were performed in the frequency range of a single transversal mode, where the associated Helmholtz equationis effectively one-dimensional and waveguide networks may serve as models of quantum graphs with the joints and waveguides corresponding to the vertices and bonds. The tetrahedral network comprises T junctions, while the honeycomb network exclusively consists of Y junctions, that join waveguides with relative angles 90^{∘} and 120^{∘}, respectively. We demonstrate that the vertex scattering matrix, which describes the propagation of the modes through the junctions, strongly depends on frequency and is nonsymmetric at a T junction and thus differs from that of a quantum graph with Neumann boundary conditions at the vertices. On the other hand, at a Y junction, similarity can be achieved in a certain frequency range. We investigate the spectral properties of closed waveguide networks and fluctuation properties of the scattering matrix of open ones and find good agreement with random matrix theory predictions for the honeycomb waveguide graph.

How close are the classical two-body potentials to abinitio calculations? Insights from linear machine learning based force matching.

In this work, we propose a linear machine learning force matching approach that can directly extract pair atomic interactions from abinitio calculations in amorphous structures. The local feature representation is specifically chosen to make the linear weights a force field as a force/potential function of the atom pair distance. Consequently, this set of functions is the closest representation of the abinitio forces, given the two-body approximation and finite scanning in the configurational space. We validate this approach in amorphous silica. Potentials in the new force field (consisting of tabulated Si-Si, Si-O, and O-O potentials) are significantly different than existing potentials that are commonly used for silica, even though all of them produce the tetrahedral network structure and roughly similar glass properties. This suggests that the commonly used classical force fields do not offer fundamentally accurate representations of the atomic interaction in silica. The new force field furthermore produces a lower glass transition temperature (Tg ∼ 1800K) and a positive liquid thermal expansion coefficient, suggesting the extraordinarily high Tg and negative liquid thermal expansion of simulated silica could be artifacts of previously developed classical potentials. Overall, the proposed approach provides a fundamental yet intuitive way to evaluate two-body potentials against abinitio calculations, thereby offering an efficient way to guide the development of classical force fields.

Raman and IR spectra of water under graphene nanoconfinement at ambient and extreme pressure-temperature conditions: a first-principles study.

The nanoconfinement of water can result in dramatic differences in its physical and chemical properties compared to bulk water. However, a detailed molecular-level understanding of these properties is still lacking. Vibrational spectroscopy, such as Raman and infrared, is a popular experimental tool for studying the structure and dynamics of water, and is often complemented by atomistic simulations to interpret experimental spectra, but there have been few theoretical spectroscopy studies of nanoconfined water using first-principles methods at ambient conditions, let alone under extreme pressure-temperature conditions. Here, we compute the Raman and IR spectra of water nanoconfined by graphene at ambient and extreme pressure-temperature conditions using ab initio simulations. Our results revealed alterations in the Raman stretching and low-frequency bands due to the graphene confinement. We also found spectroscopic evidence indicating that nanoconfinement considerably changes the tetrahedral hydrogen bond network, which is typically found in bulk water. Furthermore, we observed an unusual bending band in the Raman spectrum at ∼10 GPa and 1000 K, which is attributed to the unique molecular structure of confined ionic water. Additionally, we found that at ∼20 GPa and 1000 K, confined water transformed into a superionic fluid, making it challenging to identify the IR stretching band. Finally, we computed the ionic conductivity of confined water in the ionic and superionic phases. Our results highlight the efficacy of Raman and IR spectroscopy in studying the structure and dynamics of nanoconfined water in a large pressure-temperature range. Our predicted Raman and IR spectra can serve as a valuable guide for future experiments.

Structural Chemistry of Zeolitic Imidazolate Frameworks.

Zeolitic imidazolate frameworks (ZIFs) are a subclass of reticular structures based on tetrahedral four-connected networks of zeolites and minerals. They are composed of transition-metal ions and imidazolate-type linkers, and their pore size and shape, surface area, and functionality can be precisely controlled. Despite their potential, two questions remain unanswered: how to synthesize more diverse ZIF structures and how ZIFs differentiate from other crystalline solids. In other words, how can we use our understanding of their unique structures to better design and synthesize ZIFs? In this Review, we first summarize the methods for synthesizing a wide range of ZIFs. We then review the crystal structure of ZIFs and describe the relationship between their structure and properties using an in-depth analysis. We also discuss several important and intrinsic features that make ZIFs stand out from MOFs and discrete molecular cages. Finally, we outline the future direction for this class of porous crystals.

Effects of Hydrogen Peroxide on the Hydrogen Bonding Structure and Dynamics of Water and Its Influence on the Aqueous Solvation of the Insulin Monomer.

The hydrogen bond structure and dynamics of water and hydrogen peroxide (H2O2) in their binary mixtures have been studied at 298 K by classical molecular dynamics simulations. Twelve different concentrations of aqueous-H2O2 solutions are considered for this study. We have analyzed the interactions between water and H2O2 by site-site pair correlation functions and observed that the probability of formation of OW···HP hydrogen bonds are higher compared to OP···HW. The second solvation shell of water is strongly affected by increasing H2O2 concentrations (XP > 0.50), which signifies the destruction of the tetrahedral network structure of water. The translational and rotational dynamics of water and H2O2 do not significantly change up to 25% of H2O2 in aqueous mixtures. The hydrogen bond lifetime of water-water, water-H2O2, and H2O2-H2O2 in the aqueous-H2O2 solutions shows a very minimal change with increasing H2O2 concentrations. In addition to this, we also investigated the effect of H2O2 on the insulin monomer and observed that higher concentrations of H2O2 (XP = 0.10) change the secondary structure. The influence of H2O2 is more on chain-B than that on chain-A in the insulin monomer. The H2O2 occupancy at the protein surface is higher for negatively charged (GLU) and polar (ASN and THR) amino acid residues compared with that for positively charged and neutral residues in the solutions.

Computational Screening and Stabilization of Boron-Substituted Type-I and Type-II Carbon Clathrates.

Boron substitution represents a promising approach to stabilize carbon clathrate structures, but no thermodynamically stable substitution schemes have been identified for frameworks other than the type-VII (sodalite) structure type. To investigate the possibility for additional tetrahedral carbon-based clathrate networks, more than 5000 unique boron decoration schemes were investigated computationally for type-I and type-II carbon clathrates with a range of guest elements including Li, Na, K, Rb, Cs, Mg, Ca, Sr, and Ba. Density functional theory calculations were performed at 10 and 50 GPa, and the stability and impact of boron substitution were evaluated. The results indicate that the boron-substituted carbon clathrates are stabilized under high-pressure conditions. Full cage occupancies of intermediate-sized guest atoms (e.g., Na, Ca, and Sr) are the most favorable energetically. Clathrate stability is maximized when the boron atoms are substituted within the hexagonal rings of the large [51262]/[51264] cages. Several structures with favorable formation enthalpies <-200 meV/atom were predicted, and type-I Ca8B16C30 is on the convex hull at 50 GPa. This structure represents the first thermodynamically stable type-I clathrate identified and suggests that boron-substituted carbon clathrates may represent a large family of diamond-like framework materials with a range of structure types and guest/framework substitutions.

Order and Disorder in Mixed (Si, P)–N Networks Sr2SiP2N6:Eu2+ and Sr5Si2P6N16:Eu2+

AbstractIn the field of nitride phosphors, which are crucial for phosphor‐converted light‐emitting diodes, mixed tetrahedral networks hold a significant position. With respect to the wide range of compositions, the largely unexplored (Si, P)–N networks are investigated as potential host structures. In this work, two highly condensed structures, namely Sr2SiP2N6 and Sr5Si2P6N16 are reported to address the challenges that arise from the similarities of the network‐forming cations Si4+ and P5+ in terms of charge, ionic radius, and atomic scattering factor, a multistep workflow is employed to elucidate their structure. Using single‐crystal X‐ray diffraction, energy‐dispersive X‐ray spectroscopy (EDX), atomic‐resolution scanning transmission electron microscopy (STEM)‐EDX maps, and straightforward crystallographic calculations, it is found that Sr2SiP2N6 is the first ordered, and Sr5Si2P6N16 the first disordered, anionic tetrahedral (Si, P)–N network. After doping with Eu2+, Sr2SiP2N6:Eu2+ shows narrow cyan emission (λmax = 506 nm, fwhm = 60 nm/2311 cm−1), while for Sr5Si2P6N16:Eu2+ a broad emission with three maxima at 534, 662, and 745 nm upon irradiation with ultraviolet light is observed. An assignment of Sr sites as probable positions for Eu2+ and their relation to the emission bands of Sr5Si2P6N16:Eu2+ is discussed.

A comparative analysis of ambient-cured metakaolin geopolymer mortar and flash-calcined soil geopolymer

This paper focuses on the development of a geopolymer (GP) mortar that can be cured under ambient conditions using flash-calcined dredged sediment (FCS) and flash-calcined excavated clay (FCC), as a substitute for Metakaolin (MK). Granulated blast furnace slag (GBFS) is also added to some of the GP mixes to study its effect on GP performance. Potassium silicate (K2SiO2) was used as an alkaline reagent (AR). Therefore, this study investigates the effect of binder composition on the mechanical and durability performance of the GP mortar samples. Acid attack test, high-temperature resistance test, and microstructural analysis tests such as X-ray diffraction (XRD) and Fourier transform infrared spectroscopy (FTIR) were conducted to compare the reference mix with other substitute mixes containing FCS and FCC. Finally, the nuclear magnetic resonance (NMR) test is done on all GP mixes to verify their network classification. The results show that using FCS/FCC and only 10–20 % wt. of GBFS in the GP mortar mixes can result in similar or better properties in terms of strength and durability, while the NMR test identifies their tetrahedral network can vary between formulations.

A molecular dynamics simulations study on the modification of aqueous solution structure and dynamics in presence of monovalent salts: An electronic continuum correction approach and effect of ion size

The hydrogen bonding structure and dynamics of water are investigated by varying the concentrations up to 6.18 m for full-charged and the electronic continuum correction with rescaling (ECCR) charged model for NaCl solutions using classical molecular dynamics simulations. We have also considered the seven different (MCl/NaX) salt solutions at 6.18 m with varying monovalent cations (M+) or anions (X-). The first and second solvation shells of water in both full- and ECCR models are affected by NaCl concentrations, and destruction of the tetrahedral network structure is observed. Probability of ion pair formation is higher in KCl and NaF solutions compared to other salts at 6.18 m. The self-diffusion coefficient values of water, Na+ in full-charged, and Cl− in ECCR models are in good agreement with the experimental results. The hydrogen bond lifetime of water does not significantly change with increasing NaCl salt concentrations, but Cl−-water lifetime is significantly lowered in the ECCR model.