Middle-range Order Research Articles

Solid-state vitrification of LiPO3 through mechanical milling

A novel glass state of LiPO3 was obtained in powders produced by mechanical planetary ball milling of the crystal phase, in a direct room temperature solid-state process. X-ray diffraction shows that the amorphization develops through the compression along the [2 0 2] direction. This new material shows the calorimetric signatures of the glass state (glass transition and crystallization), and is produced in an excited state relaxing the excess of enthalpy through an exothermic event below the glass transition, akin to bulk glasses produced by hyperquenching of their melts. 31P nuclear magnetic resonance (NMR) reveals the progressive amorphization of the particles: the collapse of the resonances from P crystallographic sites and the appearance of broad resonances from amorphous domains. The nature of this glass is different from those obtained through melt-quench of bulk samples. The glass transition (Tg = 303 °C) and crystallization (Tc = 350 °C) temperatures are lower than in the melt-quenched glass (Tg = 330 °C, Tc = 379 °C). Also, 31P NMR shows a broader distribution of environments around Q2 phosphates, and higher populations of Q1 and Q3, suggesting differences in middle-range order. The amorphization can be fully reversed by recrystallization of the powders at 333 °C.

First Sharp Diffraction Peak features of the intermediate phase glasses and amorphous thin films in the non-stoichiometric (GeS4)x(AsS3)1-x system

Grazing incidence X-ray scattering (GIXRS) patterns of thin solid films based on non-stoichiometric chalcogenide glasses (ChG) from the pseudo - binary system (GeS4)x(AsS3)1-x were studied with a focus on the First Sharp Diffraction Peak (FSDP), assigned to the middle range order (MRO) of the glassy material. The films were grown using explosive thermal evaporation in vacuum (10−4 Pa) of pulverized ChG, prepared from previously synthesized bulk glasses, onto mono-crystalline silicon substrates. Scanning Electron Microscopy (SEM) and Energy-Dispersive X-ray (EDX) spectroscopy were used to examine the morphology and elemental composition of the films, which were found to have similar composition to the bulk glasses. However, it was revealed that the molecular structure of the grown amorphous films differs from that of the initial ChG bulk material, as indicated by changes in the composition-dependent position and width of the FSDP. Additionally, the intensities of the FSDP in the films were higher compared to those of the bulk samples, suggesting that the molecular-like structure of ChGs is more pronounced in the form of thin films grown from the vapor phase.

Raman scattering evidence on the correlation of middle range order and structural self-organization of As-S-Ge glasses in the intermediate phase region

The Raman scattering of bulk nonstoichiometric chalcogenide alloys along the pseudo-binary AsS3 – GeS4 tie-line, which completely lies in the intermediate phase (IP) region of As-S-Ge ternary system was investigated in order to reveal the structural transformations in charge of the unusual features of the middle range order, elastic and physical-chemical parameters of these glasses observed earlier. It is shown that very narrow compositional areas can form inside the IP with high level of structural self-organization, mainly due to sudden increase of the concentration of highly flexible species such as quasi-tetrahedral (QT) S=As(S1/2)3 s.u. that comprises 4-fold coordinated As atoms. In the (GeS4)x(AsS3)1-x ternary system such a compositional area appears around the Ge7.7As15.3S77 (x =0.33; < r > = 2.31) composition that is a strongly self-organized glass with an assessed concentration of QT S=As(S1/2)3 around 30 % of total atomic clusters being the building blocks of the structure. This composition consists of minimal number of atomic building species, apart from QT S=As(S1/2)3 s.u. and free sulfur only the AsS3 pyramids and edge-sharing (ES) GeS4 tetrahedra have been revealed. Actually this self-organized state seems to be compositionally “metastable” as the variation of Ge concentrations by approximately ±3.5at% transforms the most part of the QT S=As(S1/2)3 s.u. into either AsS3 pyramids or corner-sharing (CS) GeS4 tetrahedra, mixed with a number of others clusters of smaller concentration. A good correlation was found between the compositional dependence of Raman scattering normalized strengths and middle range ordering (MRO) parameters such as sizes of molecular domains (D) and correlated inter-domain distances (d), as well as the molar volume (Vm ) and longitudinal elastic modulus (CL). MRO parameters and molar volume exhibit global minima around composition (As15,3 S77 Ge7,7; x = 0.33; < r > = 2.31) corresponding to strong self - organized glass that assign it as glass with most “packed” MRO structure and meanwhile the elastic modulus reaches its maximum value.

MIDDLE RANGE ORDER IN GLASSES OF La2O3–Nb2O5–B2O3 AND BaO–Nb2O5–P2O5 SYSTEMS ACCORDING TO X-RAY TOTAL SCATTERING

We have obtained the X-ray total scattering patterns at wavelength 0.20735 ? and corresponding to them radial distribution functions (RDF) of electron density for glasses in the La2O3–Nb2O5–B2O3 and BaO–Nb2O5–P2O5 systems. The RDF demonstrate separate peaks at distances below ~1 nm which points on the middle range ordering in the considered glasses. The consideration of RDF for BaO–Nb2O5–P2O5 glasses system with high concentration of BaO show that the middle range order is caused by the polyhedra chains of ideal BaO crystal, and these chains does not belong to any low-index crystal plane. For La2O3–Nb2O5–B2O3 glasses system the polyhedra chains are observed which resemble those in the LaB3O6 crystal, with polyhedra bound through borate groups. For all considered glasses the niobium polyhedra does not form extended chains.

Middle range order and elastic properties of non-stoichiometric chalcogenide glasses in the AsS3 - GeS4 system

Longitudinal elastic modulus of glasses (GeS4)x (AsS3)1-x has been determined from experimentally measured density and ultrasound velocity with respect to the “first sharp diffraction peak (FSDP)” of the XRD halos, ascribed to intermediate range ordering. Quantitative analysis of FSDP allowed estimation of the size of correlated middle range ordered domains and inter domain distances dependent on glass composition. It was revealed that interdomain distance and average domains size are strongly correlated, both reaching the minimal value at composition that comprises 7,7 at.% Ge, therefore the domain concentration of this composition appears to be maximal. It was not found an apparent correlation between density or ultrasound velocity and middle range ordering parameters of the glass. However, a clearly visible correlation was found between Young’ modulus and concentration of structural domains: Young’ modulus linearly increases with domain concentration, with an exception of an only case occurring at low Ge concentration (∼x223C 4 at.%). The results are explained in terms of deep structural transformation in the middle range order caused by molecular reorganization, which controls the physical properties, including the elastic ones of the glass. The study has pointed out the light glasses of the AsS3-GeS4 system possessing enhanced elastic and sound characteristics available for application.

Disordered Cubic Spinel Structure in the Delithiated Li2MnO3 revealed By Difference Pair Distribution Function Analysis

An archetypical Li-rich layered oxide, Li2MnO3, shows a large initial charge capacity of ~350 mAh g-1 with little oxidation of the constituent Mn ions, yet, the crystal structure of delithiated Li2MnO3 is still unclarified because the structural disorder induced by the considerable Li extraction makes the analysis challenging. We have performed X-ray pair distribution function (PDF) analysis in combination with the X-ray powder diffraction (XRPD), transmission electron microscopy (TEM), and X-ray absorption spectroscopy (XAS) to reveal the disordered crystalline structure of the electrochemically delithiated Li2MnO3. The XRPD and TEM analyses clarified the formation of a low-crystallinity phase in the light of the average structure. The XAS and PDF analyses revealed that the MnO6–based framework was rearranged with maintaining the MnO6 octahedral coordination after the initial charge. The difference pair distribution function (d-PDF) technique was therefore employed to extract the structural information of the low-crystallinity disordered phase. The delithiated phase was found to have a structure similar to the cubic spinel, LiMn2O4, rather than that of delithiated LiMn2O4 (l-MnO2). In addition, the middle-range order of the delithiated phase deteriorated after the charge, indicating a decrease of coherent domain size to a single nm order. The composite structure formed after the first charge, therefore, consists of the disordered cubic spinel structure and unreacted Li2MnO3. The formation of the composite structure “activates” the electrode material structurally and eventually induces characteristic large capacity of this material.

Disordered Cubic Spinel Structure in the Delithiated Li2MnO3 Revealed by Difference Pair Distribution Function Analysis

An archetypical Li-rich layered oxide, Li2MnO3, shows a large initial charge capacity of ~350 mAh g-1 with little oxidation of the constituent Mn ions, yet, the crystal structure of delithiated Li2MnO3 is still unclarified because the structural disorder induced by the considerable Li extraction makes the analysis challenging. X-ray pair distribution function (PDF) analysis is a powerful tool to experimentally elucidate the structure of the disordered phase. Here, we conducted a comprehensive analysis with a focus on PDF analysis in combination with the X-ray powder diffraction (XRPD), transmission electron microscopy (TEM), and X-ray absorption spectroscopy (XAS) to reveal the disordered crystalline structure of the electrochemically delithiated Li2MnO3. The XRPD and TEM analyses clarified the formation of a low-crystallinity phase in the light of the average structure. The XAS and PDF analyses further revealed that the MnO6–based framework was rearranged with maintaining the MnO6 octahedral coordination after the initial charge. The difference pair distribution function (d-PDF) technique was therefore employed to extract the structural information of the low-crystallinity disordered phase. The delithiated phase was found to have a structure similar to the cubic spinel, LiMn2O4, rather than that of delithiated LiMn2O4 (λ-MnO2). In addition, the middle-range order of the delithiated phase deteriorated after the charge, indicating a decrease of coherent domain size to a single nm order. The composite structure formed after the first charge, therefore, consists of the disordered cubic spinel structure and unreacted Li2MnO3. The formation of the composite structure “activates” the electrode material structurally and eventually induces characteristic large capacity of this material.

Short- and middle-range order structures of KNbO3 nanocrystals

The atomic-scale structure of KNbO3 nanocrystals with the particle size of 115 ∼165 Å has been studied by combining Rietveld refinement and the atomic pair-distribution function (PDF) technique. We performed high-energy synchrotron X-ray scattering to extract short- and middle-range order structures. The unit cell size of the KNbO3 nanocrystals expanded as the particle size was reduced. PDF analysis of the whole nanocrystals in the initial phase of the crystal growth showed that it is close to a rhombohedral structure at the short-range order, tetragonal structure at the middle-range order, and cubic structure at the long-range order. The local structure is asymptotic to the average structure as the fitting range is elongated. The size of the region in which the local structure is same as that of the bulk, we named this the coherent length, is closely related to the average structure.

Nanometer-Sized Crystalline Clusters of IGZO Films Determined from the Grazing Incidence X-ray Scattering and Anomalous X-ray Scattering Data Combined with Reverse Monte Carlo Simulations

Grazing incidence X-ray scattering measurements have been carried out on c-axis aligned crystalline-indium gallium zinc oxide (CAAC-IGZO) film and nanocrystalline category-indium gallium zinc oxide (NC-IGZO) film and the following results were obtained: (1) the characteristic layered structure of the IGZO crystal did not hold its shape and the X-ray scattering profile showed only a relatively sharp first peak at the wave vector (Q) = 21.8 for CAAC film and 23.1 nm−1 for NC film, respectively, and additional weak broad peaks were observed at a higher angle. (2) In the case of the CAAC film, tiny peaks were observed at Q = 7 and 14 nm−1, corresponding to the positions of the 003 and 006 reflections, respectively, of the IGZO crystal. Such tiny peaks were not detected in the case of NC film but the asymmetry of the first peak at the low angle side was clearly observed. (3) These structural features implied that more than three polyhedral units, such as InOx (x = 4–6), GaOy (y = 4–6), and ZnOz (z = 4–6), were likely to coexist. It is appropriate to call this structural feature as cluster-1. (4) A composite-type structure formed by combining these polyhedral units is also likely to exist and leads to middle-range ordering. This structure is called cluster-2. The size of such cluster-2 has been estimated to be 2.2 nm for CAAC film and 1.8 nm for NC film using the measured pair distribution function. To gain insights into the structural features of IGZO films, realistic atomic-scale models were obtained to fit not only the ordinary interference function of grazing incidence X-ray scattering but also the environmental interference function of the anomalous X-ray scattering (AXS) with Zn-absorption edge using reverse Monte Carlo (RMC) simulation. (5) The resultant models indicated the complex and irregular atomic arrangements of two types of IGZO films, which are well characterized by nanometer-sized crystalline clusters. This characteristic feature may be referred to as crystalline–cluster–composite (triple C) structure.

Emergent composite structures following the amorphization of itraconazole with α-glucosyl rutin by over-grinding

We investigated the use of α-glucosyl rutin (rutin-G) as a grinding aid for wet bead milling. Itraconazole (ITCZ), which has low solubility at physiological pH conditions, was used as a model poorly water-soluble drug. Pulverization of ITCZ with rutin-G effectively improved the dissolution profile of ITCZ relative to other grinding aids, whereas excess pulverization of ITCZ with rutin-G led to a decrease in the dissolution rate of ITCZ. The structures of these pulverized samples were evaluated by powder X-ray diffraction (PXRD) and small-angle X-ray scattering (SAXS) to better understand this unexplained phenomenon. The PXRD pattern of ITCZ with rutin-G after milling for 10h was dramatically different from the patterns of ITCZ ground for shorter times. The results imply that the molecular-level middle-range ordering of the rutin-G and ITCZ mixture was almost unchanged for different milling time increments up to 5h, whereas the sample milled for 10h showed structural changes in the middle-range order. Furthermore, an analysis of the SAXS measurements suggested a change in the composite structures from large μm-size particles through a molecular-level local atomic arrangement of each particle via a molecular reaction between ITCZ and rutin-G as the milling time progressed. The decrease in dissolution rate after 5h may be related to the formation of the new composite structures between ITCZ and rutin-G. Excess pulverization caused by the addition of rutin-G may induce structural changes in the drug undergoing milling.

The MRO-accompanied modes of Re-implantation into SiO2-host matrix: XPS and DFT based scenarios

The following scenarios of Re-embedding into SiO2-host by pulsed Re-implantation were derived and discussed after XPS-and-DFT electronic structure qualification: (i) low Re-impurity concentration mode → the formation of combined substitutional and interstitial impurities with Re2O7-like atomic and electronic structures in the vicinity of oxygen vacancies; (ii) high Re-impurity concentration mode → the fabrication of interstitial Re-metal clusters with the accompanied formation of ReO2-like atomic structures and (iii) an intermediate transient mode with Re-impurity concentration increase, when the precursors of interstitial defect clusters are appeared and growing in the host-matrix structure occur. An amplification regime of Re-metal contribution majority to the final Valence Band structure was found as one of the sequences of intermediate transient mode. It was shown that most of the qualified and discussed modes were accompanied by the MRO (middle range ordering) distortions in the initial oxygen subnetwork of the a-SiO2 host-matrix because of the appeared mixed defect configurations.

Structure and properties of lead silicate glasses and melts

Viscosity, density and glass transition temperature measurements were performed on the simple PbO-SiO2 system with increasing PbO content from 5 to 70mol%. The results of these analyses have been complemented by spectroscopic studies (Raman & X-ray Absorption Spectroscopy) in order to link macroscopic properties to structural information at short- and middle-range order. A strong decrease of the viscosity is observed even with the incorporation of 5mol% PbO, and this decrease goes on with the increase of PbO content. This effect is confirmed by the continuous decrease of the glass transition temperature with increasing PbO content. Based on our interpretations of Raman spectra, which show similarities to alkali or earth-alkaline-silicate glasses, these effects appear to arise from depolymerization of the silica network. Consequently, lead acts as a network modifier even at low content. Although, it could form PbO4 tetrahedra when it is present in large quantities, it cannot be asserted that lead acts as a network former at high lead content.

Impact of pressure on plastic yield in amorphous solids with open structure.

Plasticity in amorphous silica is unusual: The yield stress decreases with hydrostatic pressure, in contrast to the Mohr-Coulomb response commonly found in more compact materials such as bulk metallic glasses. To better understand this response, we have carried out molecular dynamics simulations of plastic response in a model glass with open structure. The simulations reproduce the anomalous dependence of yield stress with pressure and also correctly predict that the plastic response turns to normal once the material has been fully compacted. We also show that the overall shape of the yield surface is consistent with a quadratic behavior predicted assuming local buckling of the structure, a point of view that fits well into the present understanding of the deformation mechanisms of amorphous silica. The results also confirm that free volume is an adequate internal variable for a continuum scale description of the plastic response of amorphous silica. Finally, we also investigate the long-range correlations between rearrangement events. We find that strong intermittency is observed when the structure remains open, while compaction results in more homogeneous rearrangements. These findings are in agreement with recent results on the effect of compression on the middle range order in silicate glasses and also suggest that the well-known volume recovery of densified silica at relatively low temperatures is in fact a form of aging.

Atomic structure of Cu–Zr–Ti metallic glasses subjected to high temperature annealing

An influence of high temperature annealing process (before crystallization) on the atomic structure of two different as-prepared ribbon Cu–Zr–Ti metallic glasses (Cu60Zr20Ti20 and Cu55Zr16Ti29, at.%) was experimentally studied by means of differential scanning calorimetry and in situ hard X-ray diffraction. Results of our experiments prove different atomic structure and behaviour of the glasses upon the annealing. Special emphasis is placed on the thermally activated effects which precede the crystallization. During the annealing, both glasses initially show with elevated temperature continuous short and middle range order thermal expansion and an overall decline of the atomic structure ordering. But above a temperature, which can be slightly different for every mean atomic neighbour (or every atomic coordination shell), one can observe a change in behaviour of the glasses: the glasses modify the thermal expansion rate of most of the mean atomic neighbours’ distances and show a tendency to increase the degree of ordering of the atomic structure. Both these effects are more pronounced for Cu55Zr16Ti29. Therefore, as a result of the metallic glasses’ different behaviour in the annealing, near the crystallization temperature Cu55Zr16Ti29 commonly shows larger relative elongation of the mean atomic neighbours’ distances (larger thermal expansion) than Cu60Zr20Ti20. Moreover, Cu55Zr16Ti29 exhibits contrary to Cu60Zr20Ti20 an increase of the degree of ordering of the atomic structure if compared with the initial as-prepared state at the beginning of the experiment.

Europium Structural Effect on a Borosilicate Glass of Nuclear Interest

Short and middle range order structure of a borosilicate glass of nuclear interest doped with europium oxide was investigated in this study. Neutron diffraction and Wide Angle X-ray Scattering were used as experimental techniques. Furthermore, Reverse Monte Carlo simulation technique was also applied to build reliable atomistic models of the different glasses involved. Simulation results show that europium is more efficiently 6-coordinated in the borosilicate glasses concerned, with a Eu-O distance of 2.31 ű 0.01 Å. Partial pair distribution functions and atom count mainly indicate that europium appears in both silicate and borate environments and that IVB/IIIB ratio decreases with europium oxide increase.

Fabrication and Structure Characterization of Quasi-2-Dimensional Amorphous Carbon Structures

Quasi-2-dimensional total amorphous and half-amorphous carbon structures are fabricated from single-layer or few-layer of graphene via high-energy electron beam irradiation. Sample structures before and after electron beam irradiation are recorded by high resolution imaging and coherent nano-area electron diffraction using transmission electron microscopy (TEM). The atomic pair distribution functions of the sample are obtained from electron diffraction patterns. In the quasi-2-dimensional amorphous carbon material, the carbon hexagonal ring structure is not the main structural feature anymore, and the low order nearest distances between carbon atoms are slightly different from that in perfect graphene. Although the sample shows a long-range disordered atomic arrangement, it still holds short-range order and even middle-range order extending to 0.5 nm, as many zigzag carbon chains remain after electron beam irradiation.

Hysteresis-free HfO 2 film grown by atomic layer deposition at low temperature

Hysteresis-free hafnium oxide films were fabricated by atomic layer deposition at 90 °C without any post-deposition annealing, and their structures and properties were compared with films deposited at 150 °C and 250 °C. The refractivity, bandgap, dielectric constant and leakage current density all increase with deposition temperature, while the growth rate and breakdown field decrease. All films are amorphous with roughly the same composition. Although the thin films deposited at the above-mentioned temperatures all show negligible hysteresis, only the 90 °C-deposited films remain hysteresis-free when the film thickness increases. The 90 °C-deposited films remain hysteresis-free after annealing at 300 °C. The hysteresis in films deposited at high temperatures increases with deposition temperature. Evidences show such hysteresis originates in the HfO 2 film instead of the interface. Based on a careful structure analysis, middle-range order is suggested to influence the trap density in the films. HfO 2 films deposited at low temperature with negligible hysteresis and excellent electrical properties have great potential for the fabrication and integration of devices based on non-silicon channel materials and in applications as tunneling and blocking layers in memory devices.

Controlled mechanochemically assisted synthesis of ZnO nanopowders in the presence of oxalic acid

In this study, the ZnO nanopowders were synthesized by mechanochemical processing with a successive thermal decomposition reaction. The initial reactants mixture of zinc chloride and oxalic acid was milled from 30 min to 4 h and thermally treated for 1 h at 450 °C. The influence of both, oxalic acid and the duration of milling, on the crystal structure, average crystallite size, average particle size, and the morphology of ZnO nanopowders were investigated. The qualitative analysis was performed using X-ray diffraction and Raman spectroscopy techniques. While the XRD analysis shows perfect long-range order and pure wurtzite structure of the synthesized ZnO powders, Raman spectroscopy indicates a different middle-range order; in addition, according to Raman spectra, it is found that lattice defects and impurities introduced in ZnO crystal structure depend on milling duration, in spite of applied thermal treatment. The particle size distribution was measured by laser diffraction, whereas the morphology of the powders was determined by scanning electron microscopy. Impurity contamination was studied using inductively coupled plasma analysis. The obtained results showed that the applied two-step method is appropriate for the synthesis of high crystalline ZnO nanopowders, with uniform spherical particles with diameter between 20 and 50 nm. Profound effect of aqueous solution of oxalic acid to prevent agglomeration of final product is presented.

10.1007/s10973-006-8228-4

The high-resolution transmission electron microscopy HRTEM study of the atomic scale mechanism of crystal structure organization within the amorphous polymeric structure of the model multicomponent glass TiO2–MgO–Al2O3–SiO2– in the glass transformation temperature range has been undertaken. In the glass transition (Tg) temperature range, glass transforms from the solid of rigid amorphous structure into viscoelastic state of weakened chemical bonds. This is an example of nuclei formation and crystal growth in the polymeric amorphous structure of low atomic scale homogeneity due to middle range ordering. It has been demonstrated that in this case crystal structure formation proceeds by successive displacement and local ordering of atoms in the amorphous structure, like disorder-order transformation in crystalline solid bodies. As the consequence in the crystallization by parent structure reorganization mechanism, traditional model of glass crystallization as well as kinetic models of reactions in solid bodies according Avrami or others, are worthy to be revised.

Relation between Local Structure and Glass Forming Ability of Liquid Alloys

An attempt has been made to describe the glass forming ability (GFA) of liquid alloys, using the concepts of the short range order (SRO) and middle range order (MRO) characterizing the liquid structure.A new approach to obtain good GFA of liquid alloys is based on the following four main factors: (1) formation of new SRO and competitive correlation with two or more kinds of SROs for crystallization, (2) stabilization of dense random packing by interaction between different types of SRO, (3) formation of stable cluster (SC) or middle range order (MRO) by harmonious coupling of SROs, and (4) difference between SRO characterizing the liquid structure and the near-neighbor environment in the corresponding equilibrium crystalline phases. The atomic volume mismatch estimated from the cube of the atomic radius was found to be a close relation with the minimum solute concentration for glass formation. This empirical guideline enables us to provide the optimum solute concentration for good GFA in some ternary alloys. Model structures, denoted by Bernal type and the Chemical Order type, were again tested in the novel description for the glass structure as a function of solute concentration. We illustrated the related energetics of the completion between crystal embryo and different types of SRO. Recent systematic measurements also provide that thermal diffusivity of alloys in the liquid state may be a good indicator of their GFA.