Intermediate Range Order Research Articles

Investigation of size effects on the structure of liquid GeSe2 calculated via first-principles molecular dynamics

The structural properties of liquid GeSe(2) have been calculated by first-principles molecular dynamics by using a periodic simulation box containing N = 480 atoms. This has allowed a comparison with previous results obtained on a smaller system size (N = 120) [M. Micoulaut, R. Vuilleumier, and C. Massobrio, Phys. Rev. B 79, 214205 (2009)]. In the domain of first-principles molecular dynamics, we obtain an assessment of system size effects of unprecedented quality. Overall, no drastic differences are found between the two sets of results, confirming that N = 120 is a suitable size to achieve a realistic description of this prototypical disordered network. However, for N = 480, short range properties are characterized by an increase of chemical order, the number of Ge tetrahedra coordinated to four Se atoms being larger. At the intermediate range order level, size effect mostly modify the low wavevector region (k ~1 Å(-1)) in the concentration-concentration partial structure factor.

Structure of jadeite melt at high pressures up to 4.9 GPa

The structure of jadeite (NaAlSi2O6) melts has been studied using multiple-angle energy-dispersive x-ray diffraction up to 4.9 GPa and 1923 K. The first sharp diffraction peak in the structure factor shifts toward higher momentum transfer as pressure increases, indicating the shrinkage of the intermediate network in the melt. The radial distribution function shows a monotonous decrease in average T-T length and T-O-T angle with increasing pressure, but displays no detectable change in the average bond length between tetrahedrally coordinated cations and oxygen (T-O length, where T = Si4+, Al3+). Our observations indicate that the dominant structural changes occur in the intermediate range order at pressures up to 4.9 GPa. The changes in T-O length, T-T length, and T-O-T angle appear to correlate with the viscosity anomaly in this pressure range.

Structural investigations of interfaces in Fe90Sc10 nanoglasses using high-energy x-ray diffraction

High-resolution diffraction experiments of Fe90Sc10 nanoglasses and rapidly quenched metallic glasses as reference materials have been performed using high-energy x-rays with a wavelength of 0.21 Å from a synchrotron radiation source. Nanoglasses are amorphous alloys with a significant fraction of interfaces on the nanometer scale. The short- and intermediate-range orders of a nanoglass are different from the well known amorphous materials produced by rapid quenching from the melt. These structural modifications have significant influence on the physical properties. In this paper, the short- and intermediate-range orders of the nanoglass Fe90Sc10 and the reference metallic glass Fe90Sc10 alloy prepared by rapid quenching are discussed.

Fabricating a Dichroic Plasmonic Mirror in Fused Silica by Dual-Ion Implantation

We describe a novel ion-implantation method for fabricating a dichroic nanoparticle film by controlling the nucleation and growth of silver nanoparticles in fused silica. We first implant Sc and O ions into the silica substrate to create a high-index layer and modify the short- and intermediate-range order; this dual-implantation technique defines a sharper interface between the silica substrate and the nanoparticle layer. By modifying the short- and intermediate-range order in a thin layer of the silica matrix, Ag ions that are subsequently implanted are subject to altered diffusion and nucleation dynamics, yielding a bilayer structure comprising spatially separated regions of smaller and larger Ag nanoparticles. Depending on the implanted dose of Sc, the peak resonant wavelength in reflectivity can shift as much as 100 nm between front-side (implanted face) and back-side (non-implanted face) illumination. Implications for the optimization of bidirectional optical filters and optical cavities are discussed and compared to calculations of scattering efficiency based on Mie theory.

Simultaneous structure and elastic wave velocity measurement of SiO2 glass at high pressures and high temperatures in a Paris-Edinburgh cell

An integration of multi-angle energy-dispersive x-ray diffraction and ultrasonic elastic wave velocity measurements in a Paris-Edinburgh cell enabled us to simultaneously investigate the structures and elastic wave velocities of amorphous materials at high pressure and high temperature conditions. We report the first simultaneous structure and elastic wave velocity measurement for SiO(2) glass at pressures up to 6.8 GPa at around 500°C. The first sharp diffraction peak (FSDP) in the structure factor S(Q) evidently shifted to higher Q with increasing pressure, reflecting the shrinking of intermediate-range order, while the Si-O bond distance was almost unchanged up to 6.8 GPa. In correlation with the shift of FSDP position, compressional wave velocity (Vp) and Poisson's ratio increased markedly with increasing pressure. In contrast, shear wave velocity (Vs) changed only at pressures below 4 GPa, and then remained unchanged at ~4.0-6.8 GPa. These observations indicate a strong correlation between the intermediate range order variations and Vp or Poisson's ratio, but a complicated behavior for Vs. The result demonstrates a new capability of simultaneous measurement of structures and elastic wave velocities at high pressure and high temperature conditions to provide direct link between microscopic structure and macroscopic elastic properties of amorphous materials.

Pressure-induced structural change of intermediate-range order in poly(4-methyl-1-pentene) melt

High-pressure in situ x-ray diffraction and specific-volume measurements on isotactic poly(4-methyl-1-pentene) melt have uncovered abrupt changes in the pressure dependence of microscopic structure as well as that of macroscopic density. The first sharp diffraction peak of the polymer melt, which is related to the intermediate-range order and is explained as resulting from the correlations between main chains, is suppressed at pressures less than 1 kbar. These changes in intermediate-range order show similarities to those seen in liquid-liquid or amorphous-amorphous transitions in simpler small molecule based systems, suggesting that this kind of phenomenon may occur in a wide range of materials.

Network Structure in GeS2–Sb2S3 Chalcogenide Glasses: Raman Spectroscopy and Phase Transformation Study

Structural order beyond the next-nearest-neighbor structural units is of great interest in network glasses, especially in chalcogenide glasses, but little specific description can be reached. Here, the structure of pseudobinary (100 – x)GeS2–xSb2S3 chalcogenide glasses is elucidated using differential scanning calorimetry, Raman scattering, and laser-induced phase transformation experiments over its full range (0 ≤ x ≤ 100) of compositions. We observe two compositional thresholds of x = 40 and 50 in the calorimetric experiments, which are confirmed by Raman scattering and laser-induced phase transformation studies, respectively. Three structural features can be derived from these results: the structural motifs in this glass network are the [SbS3] pyramid and [GeS4] tetrahedra, respectively; at x ≥ 40, the connection between [GeS4] tetrahedra vanishes; and at x ≥ 50, the aggregation of four [SbS3] units happens, preparing for the laser-induced crystallization of Sb2S3 crystallites. Combined with valuable indication from the topological thresholds, a specific structural model covering the arrangement of structural units in a large atomic scale is clarified, which can perfectly explain all the experimental results. This work provides a new way to get insight into the intermediate-range order of glass networks and understand their related physical properties.

A polymer in an ionic liquid: Effect of the length of the cationic nonpolar tail on the character of interchain correlations

On the basis of the integral equation theory, we examine spatial correlations of flexible polymer chains dissolved in an ionic liquid. The effect of the concentration of a polymer on its structural properties is studied for different lengths of the nonpolar tail of the solvent cation. The structure of a polymer-containing ionic liquid is analyzed in the reciprocal space on the basis of calculated partial structure factors. In a wide range of polymer concentrations, for all the selected values of length of the cationic nonpolar tail, long-range liquid ordering and intermediate-range liquid ordering of polymer chains are observed. The dependences of the characteristic scale of ordering of macromolecules on their number density in solution are different for ionic liquids with different lengths of the cationic nonpolar tail.

NMR studies of oxide-based glasses

Solid-state nuclear magnetic resonance (NMR) spectroscopy offers an array of options for exploring structural order of amorphous materials both over short (≲0.3 nm) and medium (≲1 nm) ranges. We review the advances reported in the literature for characterizing the structures of oxide-based glasses over roughly the past 15 years. Besides describing the current understanding of basic short-range structural aspects of binary and ternary glass systems that typically involve a single glass modifier and one (silicates and phosphates) or two (e.g., aluminosilicates, aluminophosphates and silicophosphates) network formers, we focus on illustrating the progress made for revealing intermediate-range structural order, such as extracting information about connectivities among the basic building blocks in the glass networks and how more extended structural motifs may be identified. By assuming only relatively basic background in solid-state NMR and/or the structure of glasses, we hope this review will appeal to newcomers of either area.

Mineralogy of iron microbial mats from loihi seamount.

Extensive mats of Fe oxyhydroxides and associated Fe-oxidizing microbial organisms form in diverse geochemical settings – freshwater seeps to deep-sea vents – where ever opposing Fe(II)-oxygen gradients prevail. The mineralogy, reactivity, and structural transformations of Fe oxyhydroxides precipitated from submarine hydrothermal fluids within microbial mats remains elusive in active and fossil systems. In response, a study of Fe microbial mat formation at the Loihi Seamount was conducted to describe the physical and chemical characteristics of Fe-phases using extended X-ray absorption fine structure spectroscopy, powder X-ray diffraction, synchrotron radiation X-ray total scattering, low-temperature magnetic measurements, and Mössbauer spectroscopy. Particle sizes of 3.5–4.6 nm were estimated from magnetism data, and coherent scattering domain (CSD) sizes as small as 1.6 nm are indicated by pair distribution function (PDF) analysis. Disorder in the nanostructured Fe-bearing phases results in limited intermediate-range structural order: less than that of standard two-line ferrihydrite (Fh), except for the Pohaku site. The short-range ordered natural Fh (FhSRO) phases were stable at 4°C in the presence of oxygen for at least 1 year and during 400°C treatment. The observed stability of the FhSRO is consistent with magnetic observations that point to non-interacting nanoparticles. PDF analyses of total scattering data provide further evidence for FhSRO particles with a poorly ordered silica coating. The presence of coated particles explains the small CSD for the mat minerals, as well as the stability of the minerals over time and against heating. The mineral properties observed here provide a starting point from which progressively older and more extensively altered Fe deposits may be examined, with the ultimate goal of improved interpretation of past biogeochemical conditions and diagenetic processes.

Protic ionic liquids with fluorous anions: physicochemical properties and self-assembly nanostructure

A series of 11 new protic ionic liquids with fluorous anions (FPILs) have been identified and their self-assembled nanostructure, thermal phase transitions and physicochemical properties were investigated. To the best of our knowledge this is the first time that fluorocarbon domains have been reported in PILs. The FPILs were prepared from a range of hydrocarbon alkyl and heterocyclic amine cations in combination with the perfluorinated anions heptafluorobutyrate and pentadecafluorooctanoate. The nanostructure of the FPILs was established by using small- and wide-angle X-ray scattering (SAXS and WAXS). In the liquid state many of the FPILs showed an intermediate range order, or self-assembled nanostructure, resulting from segregation of the polar and nonpolar hydrocarbon and fluorocarbon domains of the ionic liquid. In addition, the physicochemical properties of the FPILs were determined including the melting point (T(m)), glass transition (T(g)), devitrification temperature (T(c)), thermal stability and the density ρ, viscosity η, air/liquid surface tension γ(LV), refractive index n(D), and ionic conductivity κ. The FPILs were mostly solids at room temperature, however two examples 2-pyrrolidinonium heptafluorobutyrate (PyrroBF) and pyrrolidinium heptafluorobutyrate (PyrrBF) were liquids at room temperature and all of the FPILs melted below 80 °C. Four of the FPILs exhibited a glass transition. The two liquids at room temperature, PyrroBF and PyrrBF, had a similar density, surface tension and refractive index but their viscosity and ionic conductivity were very different due to dissimilar self-assembled nanostructure.

Comparing intermediate range order for alkyl- vs. ether-substituted cations in ionic liquids

X-ray scattering data from four pairs of ionic liquids (ILs) are compared. The alkyl-substituted cations show a first sharp diffraction peak between 3 and 4 nm(-1) that is not observed for ILs having cations with ether- or hydroxy-substitutions. These observations indicate a significant difference in the intermediate range order for these liquids.

Structural characterization of titanium-doped Bioglass using isotopic substitution neutron diffraction

Melt quenched silicate glasses containing calcium, phosphorus and alkali metals have the ability to promote bone regeneration and to fuse to living bone. Of these glasses 45S5 Bioglass® is the most widely used being sold in over 35 countries as a bone graft product for medical and dental applications; particulate 45S5 is also incorporated into toothpastes to help remineralize the surface of teeth. Recently it has been suggested that adding titanium dioxide can increase the bioactivity of these materials. This work investigates the structural consequences of incorporating 4 mol% TiO(2) into Bioglass® using isotopic substitution (of the Ti) applied to neutron diffraction and X-ray Absorption Near Edge Structure (XANES). We present the first isotopic substitution data applied to melt quench derived Bioglass or its derivatives. Results show that titanium is on average surrounded by 5.2(1) nearest neighbor oxygen atoms. This implies an upper limit of 40% four-fold coordinated titanium and shows that the network connectivity is reduced from 2.11 to 1.97 for small quantities of titanium. Titanium XANES micro-fluorescence confirms the titanium environment is homogenous on the micron length scale within these glasses. Solid state magic angle spinning (MAS) NMR confirms the network connectivity model proposed. Furthermore, the results show the intermediate range order containing Na-O, Ca-O, O-P-O and O-Si-O correlations are unaffected by the addition of small quantities of TiO(2) into these systems.

Structural Changes in Vitreous GeSe4 under Pressure

High-energy X-ray diffraction experiments have been performed on GeSe{sub 4} glass up to pressures of 8.6 GPa, and the equation of state has been measured up to 10 GPa. The X-ray structure factors reveal a decrease in the first sharp diffraction peak intensity and broadening with pressure, which signifies a break-up of the intermediate range order in the glass. In contrast, the principal peak in the structure factor shows an increase in intensity and a sharpening with pressure, which is attributed to an increase in extended range order and coherence of the compacted units. The average nearest neighbor coordination number is found to remain constant in GeSe{sub 4} glass (within experimental error) over the pressure range measured. This is in contrast with the gradual increase found in GeSe{sub 2} glass. Rather, in GeSe{sub 4} glass the densification mechanism is shown to be associated with large inward shifts of the second neighbor and higher coordination shells. These features appear as additional correlations at 3.3 and 5.3 {angstrom} in the differences taken between adjacent pair distribution functions with increasing pressure.

Charge ordering and intermediate range order in ammonium ionic liquids

Molecular dynamics simulations were performed for ionic liquids based on the bis(trifluoromethylsulfonyl)imide anion, [NTf(2)], and ammonium cations with increasing length of the alkyl chain and ether functionalized chain. The signature of charge ordering is a sharp peak in the charge-charge structure factor, S(qq)(k), whose intensity is barely affected for longer carbon chain in tetraalkylammonium systems, but decreases in ether functionalized ionic liquids. The first sharp diffraction peak (FSDP) and the corresponding intermediate range order (IRO) are observed in the total S(k) of ionic liquids containing ammonium cations with relatively long chains. The intensity of the FSDP is lower in the total S(k) of the ether derivative in comparison with the tetraalkylammonium counterpart of the same chain length. It is shown that the nature of the IRO is structural heterogeneity of polar and non-polar domains, even though domains defined by chain interactions in the ether derivatives become more polar. Charge correlation in the ether derivative is modified because cations can be coordinated by oxygen atoms of the ether functionalized chain of neighboring cations.

Recent developments of anomalous X‐ray scattering for non‐crystalline materials with help of reverse Monte Carlo modeling: The example of GeSe2 glass

AbstractAnomalous X‐ray scattering (AXS) experiments on glassy GeSe2 were carried out at energies close to the Ge and Se K absorption edges in order to explore the atomic structure in the short‐ and intermediate‐ranges. The partial structure factors, Sij(Q), and the corresponding partial pair‐distribution functions, gij(r), obtained with help of reverse Monte Carlo (RMC) modeling, are in good agreement with the experimental results from neutron diffraction employing isotopic substitution (NDIS), and with the theoretical data from ab initio molecular dynamics simulation. The prepeak in the total structure factor, S(Q), indicating the existence of intermediate‐range order (IRO), does not only result from Ge–Ge atomic correlations, but also contains Ge–Se correlations. From the atomic configuration obtained from RMC modeling, several structural parameters are discussed, such as partial coordination numbers, connections of the Ge(Se1/2)4 tetrahedra, and bond angle distributions.

Structural properties of liquid Ge2Se3: A first-principles study

The structural properties of liquid Ge${}_{2}$Se${}_{3}$were investigated by first-principles molecular dynamics using the Becke-Lee-Yang-Parr scheme for the treatment of the exchange-correlation functional in density functional theory. Our data for the total neutron structure factor and the total pair-distribution function are in excellent agreement with the experimental results. The structure is made predominantly ($\ensuremath{\sim}$61%) from units comprising fourfold coordinated Ge atoms in the form of Ge-GeSe${}_{3}$ or Ge-Se${}_{4}$ motifs, but there is also a large variety of motifs in which Ge and Se are not fourfold and twofold coordinated, respectively. The miscoordinated atoms and homopolar bonds lead to a highly perturbed tetrahedral network, as reflected by diffusion coefficients that are larger than in the case of liquid GeSe${}_{2}$. The network does, nevertheless, exhibit intermediate range order which is associated with the Ge-Ge correlations and which manifests itself by a first sharp diffraction peak in the total neutron structure factor. The evolution of the properties of Ge${}_{x}$Se${}_{1\ensuremath{-}x}$ liquids (0 $\ensuremath{\le}x\ensuremath{\le}$ 1) with composition is discussed.

Combining the Pair Distribution Function and Computational Methods To Understand Lithium Insertion in Brookite (TiO2)

X-ray pair distribution function (PDF) methods and first-principles calculations have been combined to probe the structure of electrochemically lithiated TiO(2) Brookite. Traditional powder diffraction studies suggest that Brookite amorphizes upon lithium insertion, with the Bragg reflections disappearing. However, PDF analysis indicates that the TiO(2) framework connectivity is maintained throughout lithium intercalation, with expansions along the a and b axes. The Li(+) ions within the framework are poorly observed in the X-ray PDF, which is dominated by contributions from the more strongly scattering Ti and O atoms. First-principles calculations were used to identify energetically favorable Li(+) sites within the Brookite lattice and to develop a complete structural model of the lithiated material. This model replicates the local structure and decreased intermediate range order observed in the PDF data. The analysis suggests that local structural distortions of the TiO(2) lattice accommodate lithium in five-coordinate sites. This structural model is consistent with the observed electrochemical behavior.

Structural and vibrational relaxations at spontaneous aging in glass

The entropy change of intermediate-range orders (IROs) through the glass transition is discussed on the basis of the theories developed by Adam–Gibbs and Prigogine. It is estimated that the time dependence of the configurational entropy of glass is zero, but that of its vibrational entropy shows a constant decrease with the smallest change, while maintaining a constant fictive temperature and an isostructural state. It is shown that the spontaneous aging of well annealed glass shows a vibrational relaxation with a long relaxation time, while the annealing and physical aging of glass show a structural relaxation with a short relaxation time. The results indicate that the volume of glass decreases at a constant time rate through spontaneous aging at a constant temperature. It is emphasized that the existence of the constant configurational entropy below the glass transition temperature is the basic feature of glass forming. The nanoorder-size of the IROs in glass determines the residual entropy. The time symmetry in glass is spontaneously violated. The glass transition is a nano-emergence through the abrupt decrease in the fluctuations in the supercooled liquid state.

Taking Atomistic Insight into the Nanoscale: Nimrod, the Near and Intermediate Range Order Diffractometer

It is no accident that the start of the 21st century has seen significant growth in the field of nanotechnology across all the sciences. The nanoscale is the realm of the molecule, where physics, chemistry and biology meet, and where the potential for engineering control of structures containing tens to thousands of atoms is just beginning to be realised. Myriad examples of nanotechnology's existing and potential impact range from the creation of new designer drugs, through the development of hydrogen storage materials, to state-of-the-art silicon technology. This is the science that underpins the rationale for the construction of the near and intermediate range order diffractometer, Nimrod, on the ISIS second target station.